Ok... I figured it out:

func textToImage(drawText: NSString, inImage: UIImage, atPoint: CGPoint) -> UIImage{


// Setup the font specific variables
var textColor = UIColor.whiteColor()
var textFont = UIFont(name: "Helvetica Bold", size: 12)!


// Setup the image context using the passed image
let scale = UIScreen.mainScreen().scale
UIGraphicsBeginImageContextWithOptions(inImage.size, false, scale)


// Setup the font attributes that will be later used to dictate how the text should be drawn
let textFontAttributes = [
NSFontAttributeName: textFont,
NSForegroundColorAttributeName: textColor,
]


// Put the image into a rectangle as large as the original image
inImage.drawInRect(CGRectMake(0, 0, inImage.size.width, inImage.size.height))


// Create a point within the space that is as bit as the image
var rect = CGRectMake(atPoint.x, atPoint.y, inImage.size.width, inImage.size.height)


// Draw the text into an image
drawText.drawInRect(rect, withAttributes: textFontAttributes)


// Create a new image out of the images we have created
var newImage = UIGraphicsGetImageFromCurrentImageContext()


// End the context now that we have the image we need
UIGraphicsEndImageContext()


//Pass the image back up to the caller
return newImage


}

To call it, you just pass in an image:

textToImage("000", inImage: UIImage(named:"thisImage.png")!, atPoint: CGPointMake(20, 20))

The following links helped me get this straight:

Swift - Drawing text with drawInRect:withAttributes:

How to write text on image in Objective-C (iOS)?

The original goal was to create a dynamic image that I could use in an AnnotaionView such as putting a price at a given location on a map and this worked out great for it. Hope this helps someone trying to do the same thing.

For Swift 3:

 func textToImage(drawText text: NSString, inImage image: UIImage, atPoint point: CGPoint) -> UIImage {
let textColor = UIColor.white
let textFont = UIFont(name: "Helvetica Bold", size: 12)!


let scale = UIScreen.main.scale
UIGraphicsBeginImageContextWithOptions(image.size, false, scale)


let textFontAttributes = [
NSFontAttributeName: textFont,
NSForegroundColorAttributeName: textColor,
] as [String : Any]
image.draw(in: CGRect(origin: CGPoint.zero, size: image.size))


let rect = CGRect(origin: point, size: image.size)
text.draw(in: rect, withAttributes: textFontAttributes)


let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}

For Swift 4:

 func textToImage(drawText text: String, inImage image: UIImage, atPoint point: CGPoint) -> UIImage {
let textColor = UIColor.white
let textFont = UIFont(name: "Helvetica Bold", size: 12)!


let scale = UIScreen.main.scale
UIGraphicsBeginImageContextWithOptions(image.size, false, scale)


let textFontAttributes = [
NSAttributedStringKey.font: textFont,
NSAttributedStringKey.foregroundColor: textColor,
] as [NSAttributedStringKey : Any]
image.draw(in: CGRect(origin: CGPoint.zero, size: image.size))


let rect = CGRect(origin: point, size: image.size)
text.draw(in: rect, withAttributes: textFontAttributes)


let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}

For Swift 5:

func textToImage(drawText text: String, inImage image: UIImage, atPoint point: CGPoint) -> UIImage {
let textColor = UIColor.white
let textFont = UIFont(name: "Helvetica Bold", size: 12)!


let scale = UIScreen.main.scale
UIGraphicsBeginImageContextWithOptions(image.size, false, scale)


let textFontAttributes = [
NSAttributedString.Key.font: textFont,
NSAttributedString.Key.foregroundColor: textColor,
] as [NSAttributedString.Key : Any]
image.draw(in: CGRect(origin: CGPoint.zero, size: image.size))


let rect = CGRect(origin: point, size: image.size)
text.draw(in: rect, withAttributes: textFontAttributes)


let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}

You can also do a CATextLayer.

    // 1
let textLayer = CATextLayer()
textLayer.frame = someView.bounds


// 2
let string = String(
repeating: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce auctor arcu quis velit congue dictum. ",
count: 20
)


textLayer.string = string


// 3
let fontName: CFStringRef = "Noteworthy-Light"
textLayer.font = CTFontCreateWithName(fontName, fontSize, nil)


// 4
textLayer.foregroundColor = UIColor.darkGray.cgColor
textLayer.isWrapped = true
textLayer.alignmentMode = kCAAlignmentLeft
textLayer.contentsScale = UIScreen.main.scale
someView.layer.addSublayer(textLayer)

https://www.raywenderlich.com/402-calayer-tutorial-for-ios-getting-started

My simple solution:

func generateImageWithText(text: String) -> UIImage? {
let image = UIImage(named: "imageWithoutText")!


let imageView = UIImageView(image: image)
imageView.backgroundColor = UIColor.clear
imageView.frame = CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height)


let label = UILabel(frame: CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height))
label.backgroundColor = UIColor.clear
label.textAlignment = .center
label.textColor = UIColor.white
label.text = text


UIGraphicsBeginImageContextWithOptions(label.bounds.size, false, 0)
imageView.layer.render(in: UIGraphicsGetCurrentContext()!)
label.layer.render(in: UIGraphicsGetCurrentContext()!)
let imageWithText = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return imageWithText
}

For swift 4:

func textToImage(drawText text: NSString, inImage image: UIImage, atPoint point: CGPoint) -> UIImage {




let scale = UIScreen.main.scale
UIGraphicsBeginImageContextWithOptions(image.size, false, scale)


image.draw(in: CGRect(origin: CGPoint.zero, size: image.size))


let rect = CGRect(origin: point, size: image.size)


let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.alignment = .center






let attrs = [NSAttributedStringKey.font: UIFont(name: "Helvetica Bold", size: 12)!,NSAttributedStringKey.foregroundColor : UIColor.white , NSAttributedStringKey.paragraphStyle: paragraphStyle]




text.draw(with: rect, options: .usesLineFragmentOrigin, attributes: attrs, context: nil)






let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()


return newImage!
}

I have created an extension for using it everywhere :

import Foundation
import UIKit
extension UIImage {


class func createImageWithLabelOverlay(label: UILabel,imageSize: CGSize, image: UIImage) -> UIImage {
UIGraphicsBeginImageContextWithOptions(CGSize(width: imageSize.width, height: imageSize.height), false, 2.0)
let currentView = UIView.init(frame: CGRect(x: 0, y: 0, width: imageSize.width, height: imageSize.height))
let currentImage = UIImageView.init(image: image)
currentImage.frame = CGRect(x: 0, y: 0, width: imageSize.width, height: imageSize.height)
currentView.addSubview(currentImage)
currentView.addSubview(label)
currentView.layer.render(in: UIGraphicsGetCurrentContext()!)
let img = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return img!
}


}

Usage : Anywhere on your ViewController where you have the size and the label to add use it as follows -

let newImageWithOverlay = UIImage.createImageWithLabelOverlay(label: labelToAdd, imageSize: size, image: editedImage)

I can't see anything in your initial question suggesting that this must be done exclusively in code - so why not simply add a UILabel in interface builder, and add constraints to give it the same length and width as your image, center it vertically and horizontally (or however you need it placed), delete the label text, set the text font, size, colour, etc. as needed (including ticking Autoshrink with whatever minimum size or scale you need), and ensure it's background is transparent.

Then just connect it to an IBOutlet, and set the text in code as needed (e.g. in viewWillAppear, or by using a ViewModel approach and setting it on initialisation of your view/viewcontroller).

I have tried this basic components. Hope it will work.

func imageWithText(image : UIImage, text : String) -> UIImage {


let outerView = UIView(frame: CGRect(x: 0, y: 0, width: image.size.width / 2, height: image.size.height / 2))
let imgView = UIImageView(frame: CGRect(x: 0, y: 0, width: outerView.frame.width, height: outerView.frame.height))
imgView.image = image
outerView.addSubview(imgView)


let lbl = UILabel(frame: CGRect(x: 5, y: 5, width: outerView.frame.width, height: 200))
lbl.font = UIFont(name: "HelveticaNeue-Bold", size: 70)
lbl.text = text
lbl.textAlignment = .left
lbl.textColor = UIColor.blue


outerView.addSubview(lbl)


let renderer = UIGraphicsImageRenderer(size: outerView.bounds.size)
let convertedImage = renderer.image { ctx in
outerView.drawHierarchy(in: outerView.bounds, afterScreenUpdates: true)


}
return convertedImage
}

It's also possible to use the QLPreviewController. Just save the imageFile to an url like the applicationsDocuments directory under the .userDomainMask and open the apple' editor. You can draw, add shapes, arrow and even your signature. I explained the implementation in detail in the following post: https://stackoverflow.com/a/68743098/12035498