How to merge text & image (into a new image)?

[This could be either plugin or hack, not sure…]

I can program pretty well in PHP/Perl, and am hosting my own blogs on Linux.

-I want to give users printable certificates, but I don’t want to go through the process of doing it manually in PS, Paint.Net, etc.
-The only thing that will change is their name, and even that is always placed on the image in the same place, size, font, etc.
-Ideally I’d like the user to enter the text to be used on their certificate in a form text field, but I see just as many advantages to using their logged in name [picked up as a page/system variable].
-I would have an image of the certificate stored, and when they clicked “OK”, or whatever, the new image wold be created, and somehow made available to them (I could even use their user email address if need be, and email it to them).

Really, it’s as simple as that.

I have tried looking for watermarking, but this requires a pre-created image to be placed over the background. I’ve tried searching for annotate, but folks confuse annotate with annotations, and of course you can’t print something with mouseover JAVASCRIPT events.

So just imagine that you completed a course. Think meme generator but way simpler. You log onto the course’s blog, and you go to print out your certificate/diploma. You can enter a more formal title/name for yourself, or opt for your username (which may not be your real name, like mine here isn’t).

So really, I have never written anything for WordPress myself at all. I have always found plugins that did the trick. I don’t know if I’m looking for the ideal plugin, or whether I need to modify one, or whether I have to write something from scratch (yuk!).

Any advice, pointers, etc. very much appreciated!

TIA!