Welcome to Android Central! Unfortunately, it sounds like those photos got corrupted, either from the data transfer, or due to the card itself. SD cards are inherently less reliable than onboard memory, so they should never be used as the sole storage for important data -- always back it up to a more reliable storage space, like a computer hard drive or a cloud storage.
Go to
Settings>Storage, tap Unmount, then remove the card. Insert it into a PC's SD reader, and see if the photos display normally there. If so, back up all of the photos to the computer drive, then run chkdsk to look for any bad sectors on the card:
http://forums.androidcentral.com/amb...d-sd-card.html