Image Comparison

How do you successfully compare two images?

I have this image first take a screenshot the "live" image and then compare it to a reference image. It dosen't compare. Now I noticed that the pixel format is different so I scratched hashing the files with SHA and tried converting the image into B/W and using LockBits to store it in an array and try comparing the arrays to eachother. Fail too. Now I tried using it so it would loop through each item in the array. It still fails. I looked into the variables, it looks like the numbers are off by 1 or 2. It seems like I haven't filtered it enough. But I've already filitered through a brightness filter, making it a binary image, then pixalate it so it would get an "average" of the pixels to reduce noise (noise was made around the text because nexon's Scrnshot save meathod apparently comprsses the Jpg which produces some noise.

Any filters or more tolerant filtering options? I perfer C# but VB.net code would be fine as well. Or pseudo code.