Welcome to Android Central! Are the photos stored in Internal Storage, or on an external SD card? If they're on an SD card, there could be some file corruption going on, which might make the Gallery app crash. Try removing the SD card and inserting it into your computer. You can then backup your photos and delete any you don't want. You might also consider reformatting the card, in case it's corrupted somehow.
If the photos are in Internal Storage, then try going to the App Manager, select Gallery, and Clear Cache and Clear Data. Then open Gallery again, and wait for the thumbnails to repopulate. See if it keeps crashing.
It wouldn't hurt to clear the system cache partition as well, which can sometimes help with random problems like this. You won't lose any personal data.
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