Did you move them to the SD card while the card was in this phone? Or was it done on another phone, camera, computer? If done from the phone you are now trying to view them on, you should be able to go into the phones gallery and access them through there.
If for some reason it will not find them, and you moved them from the current phone to the SD card, then you may need to move them off the card to a computer, and then back onto the phone. The card may have problems.
However, if you put the pictures on the card another way, not moved there from the current phone, then it is possible that your phone just can't read them. Again, the best option then would be to move them to a computer and then back onto the phone itself. Then from the phone you can move them over to the card.