You may also need follow the guide below.
If you really deleted them and do not have a backup, they are gone. There is an off-chance (very off) that if you put the SDcard into a PC you might be able to use a data retrieval program to get them back. But success at this point is very unlikely. When you use the phone you are overwriting old deleted data thereby making it irretrievable.
The thumbnail views you see are probably in the SDcard/DCIM/.thumbnails folder. In the DCIM folder is also the 100MEDIA directory. This is where your full camera images are stored. You might want to check there, manually.
Also, make sure you didn't just accidentally change the gallery settings and possibly didn't delete them at all (i.e. Gallery | Menu | Show/Hide Items.
