I just ran my N900 through USB mode and tested the program Diskdigger (but I assume any similar program will work too), and it recovered several images i had deleted. Maybe you can give it a quick scan and see.

Edit: while i didn't delete any images recently, the ones it did recover were damaged, hopefully your images are not the same.

Edit 2: Diskdigger seems a little buggy at times, it recovered an image very well that i delete on purpose for testing, but then it lost it again (couldn't display the preview or even save it). Rescanning brought it back. Not sure whats happening, but you may want to try with more than one program and see