Here are a few tools that enable you to add text to your image without needing to use a special software program. You can do it all online and then add your photo to wdydwyd.
Be careful... some of the fonts on this are cheezy.
http://www.tagsmaker.com (Please DO NOT use this site's prefab images... upload your own photos that you take)
Can I use ANY image I find on the web? — No. Sorry, but you can't use copyrighted images. It's much better to make your own images. But,if you're doing a mash up, here's how you can find Creative Commons images.