Dear expert,
I want to compare two images. I've no idea of image processing. please help me from where to start. Do image comparison follow some standard algorithms? what are all the possible ways of image comparison? how do industrialists do? please help....

There are two answers:
1. If you are comparing two image objects that are created with the exact same colorspace and compression then you can try getting the pixels as arrays and compare pixels.
2. You will have to readup on image processing algorithms to do a content comparision.
More info in this thread