Originally Posted by Cdesja5
This feature was added last year and it's free specifically for photo uploads (adds any space used for photos to your pre-existing Dropbox limit) as opposed to Picassa which is subscription based above the 1 gb limit.
This depends on how you want to use it
If you want to store your full size photos online, then Dropbox is the better option as you get more space, upload also does the full size photos (not sure if this is optional)
With Picasa, if you use the web optimised size of photo (upto 2048x2048) when storing pictures there (I only use for sharing, not as a backup), then it is unlimited
I use Dropbox autoupload, just as a backup for my photos I take
I use Picasa autoupload/gallery for sharing pictures (mainly because of unlimited)