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I am trying to write a function to determine whether two equal-size bitmaps are identical or not. The function I have right now simply compares a pixel at a time in each bitmap, returning false at the first non-equal pixel. While this works, and works well for small bitmaps, in production I'm going to be using this in a tight loop and on larger images, so I need a better way. Does anyone have any recommendations? The language I'm using is C# by the way - and yes, I am already using the .LockBits method. =) Edit : I've coded up implementations of some of the suggestions given, and here are the benchmarks. The setup: two identical (worst-case) bitmaps, 100x100 in size, with 10,000 iterations each. Here are the results: CompareByInts (Marc Gravell) : 1107ms CompareByMD5 (Skilldrick) : 4222ms CompareByMask (GrayWizardX) : 949ms In CompareByInts and CompareByMask I'm using pointers to access the memory directly; in the MD5 method I'm using Marshal.Copy to retrieve a byte array and pass that as an argument to MD5.ComputeHash. CompareByMask is only slightly faster, but given the context I think any improvement is useful. Thanks everyone. =) Edit 2 : Forgot to turn optimizations on - doing that gives GrayWizardX's answer even more of a boost: CompareByInts (Marc Gravell) : 944ms CompareByMD5 (Skilldrick) : 4275ms CompareByMask (GrayWizardX) : 630ms CompareByMemCmp (Erik) : 105ms Interesting that the MD5 method didn't improve at all. Edit 3 : Posted my answer (MemCmp) which blew the other methods out of the water. o.O

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