How to add text to an image and users can also saved the image with the added text?

Again I've been finding the solution for this, if you're not understand my question, here's some demonstration.

I set my name as "Peter"

and I have a congratulation poster which has a space for put a name in it

when the user reach this page, the poster will generate the name and the poster and they can save both of the picture with the text in it. ** I have no demonstration code for this because I really have no idea how to do it. and I wish there's a possible way to do it as well...