I took the somewhat longer route, which I’m detailing just in case it’s useful to anyone (I’m always curious about how people did stuff). I used iPhoto to crop an old picture that I’d scanned from a photo album. I exported it in order to save it as a smaller size file–about 800 by 600 pixels. Then I cut and pasted the exported photo into an Appleworks Paint document, used that to put the text in, saved the whole thing as a .jpg, and uploaded it to Flickr. Not as snazzy as Photoshop, no doubt, but hey, it was free.
You can read the original call for submissions at LISNews.org.