You are re-allocating (thus clearing all it's contents) your array
each time you go trough the loop.
array = [[NSMutableArray alloc]init];
int j;
for (j=0; j<6; j++)
{
UIImageView *imageView = [_imageArray objectAtIndex:j];
[array addObject:[NSValue valueWithCGRect:imageView.frame]];
NSLog(@"%d",[array count]);
}