There’s a great site called Superlame (www.superlame.com) that let’s you do exactly that. Just upload any photo that is on your hard drive now and you can add some speech bubbles to it. Then you can put it on your web page, Facebook, email, or wherever you want to use it.
Here’s an example. This photo is sort of interesting, in a “Deliverance” kind of way.
You may have noticed – the speech bubbles can even extend outside the actual boundaries of the picture. You can also change the font, font size, whether the characters are speaking or thinking, and other options.
Superlame.com is free but welcomes donations.