Well if you took the photos from the phone, you should be able to see them in your gallery.
If you took them on say a different phone while the SD card was in the different phone, then it is possible that your phone can't view them. If that particular card was turning into "Internal" storage on a different phone it would have been encoded to that device and not be viewable on others.
If this isn't the case, try connecting your phone to a computer and see if you can view what is on the SD card. If yes, then you can move it all over to the computer, eject the SD card from the phone and reinstall it, and then copy the stuff back over to the SD card by plugging the phone back into the computer. Then it should be viewable by the gallery on...