iphone - Generate hash from UIImage

Question

I'm trying to compare two UIImages from the file system to see if they are the same. Obviously, I can't use NSObject's hash method, since this returns a hash of the object, and not the actual image data.

I found code generate an MD5 hash from a string, but I haven't discovered how to implement it for a UIImage.

How should I go about hashing a UIImage? Or is my method for comparing to images totally off?

Answer 1

I wound up using the following code to accomplish the task. Note that this requires that you import <CommonCrypto/CommonDigest.h>:

unsigned char result[CC_MD5_DIGEST_LENGTH];
NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(inImage)];
CC_MD5([imageData bytes], [imageData length], result);
NSString *imageHash = [NSString stringWithFormat:
                       @"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",
                       result[0], result[1], result[2], result[3], 
                       result[4], result[5], result[6], result[7],
                       result[8], result[9], result[10], result[11],
                       result[12], result[13], result[14], result[15]
                       ];