I 've use 

```
NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(inImage)];

CC_MD5(imageData, [imageData length], result);

```

for generate **MD5** code of my picture and add them to **NSDictionary** for compare the image from photoLibrary.
But when I add some code or reboot my device , I find the hash code is totally changed .
How can resolve this problem ?