ImageMagick will work just fine, and is free. It may be a bit complex for many folks, though. Don't forget, however, that you can also use just about any graphics program for this. Just type the text how you want it to appear, and save it out as a JPEG, GIF, or PNG image as appropriate. You can even use MS Word's Copy as Picture command, though you have a lot less control, then. If you want to automate the process a bit, you could write up some VBScript to drive an Office app, or, if on a Mac, some AppleScript to drive any drawing program. But then, we're back to a bit more complexity, so we may also be back to ImageMagick....
I would bet that there are little single-purpose utilities out there for doing this sort of thing, but unfortunately, I'm not familiar with any.
BTW, I don't know exactly what's being generated, but you most likely don't need to generate hundreds of images if you just generate and then combine parts. For example, you might generate the ten digits, the separator character(s), and the month names, for a total of about 23 images. Without the month names, you're down to just 11 images. If this will work in this particular situation, it'll save a lot of time.
