Hi!
I actually had the same problem when using picasa... but I think I figured out what was wrong. When you upload pics to the web using picasa you can choose a size (small, medium, or large). My theory is that the size is stuck after you've uploaded it. If there is one specific one you want to post I'd try re-uploading and making sure that you've picked a larger size during the uploading process
I hope that works for you!
Meredith