What app are you using? Stock gallery app - if so what android version? (gingerbread, ics...later? (might be helpful since we don't have that device...)
Something to consider - and may be what is the case - they could be pictures no longer there.
A thumbnail of each picture is saved into a thumbnails database - once there it kinda becomes independent of the picture. The gallery is actually displaying whatever is in the thumbnails database, and could be showing pictures long gone. It does happen at times.
I like to use QuickPic as my gallery app (it's awesome!) and it stores the thumbnail database in /sdcard/Android/data/com.alensw.PicFolder
See if you can track down the thumbnail database for your gallery app and (back it up first!!!!!!!!!) delete it.
Next time you open the gallery app it should generate a new, current thumbnail database showing you more accurately what is on the device.
After that, long press on a specific picture in the gallery might get you a pop up menu you can select a details or properties option from? That should tell you (one at a time...) where to find each picture.
Note: thumbnails are tiny, low resolution copies of the picture and not what you want to end up with, just one clue on the path of finding what you are looking for.
Hope this helps some.
