insertObject:atIndex:

gistfile1.m

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSMutableArray *recents = [defaults objectForKey:RECENT_PHOTO_KEY];
if (!recents) recents = [NSMutableArray array];
    
if ([recents containsObject:clickedPhoto]) [recents removeObject:clickedPhoto]; //deleting object if we have one to keep the array of unique objects
    
[recents insertObject:clickedPhoto atIndex:0]; //inserting clicked photo to the beginning of the mutable array
[defaults setObject:recents forKey:RECENT_PHOTO_KEY]; //saving defaults
[defaults synchronize];