How can I format my gallery (S3 GT-I9300I)?

[AC Question]

some photos & video in my S3 GT-I9300I gallery that not be deleted . I do many changes in the settings but not success .

 

[B. Diddy]

Welcome to Android Central! Are they photos you took, or do they look like images used by apps, or downloaded from the web? The Gallery will display all images stored on the phone--even those used by apps and cached from web browsing--unless the directory with the images has a ".nomedia" file in it.

The other possibility is that those photos are stored in your Google+ Photos cloud album. Do the thumbnails have a Picasa or Google+ Photos icon on them?