how to write code for correlation of two image in c++ using open cv lib

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Well you need to tell us what exactly you what you want to compare - be specific. This is too broad i think.

1. If you want to look if two images are the "same" - use template matching
2. If you want to compare for occurrence of object - use object detection
3. If you want to compare for identity - you would need to use a neuronal network with embeddings most likely

And these are only 3 rough possibilities what to do in computer vision. But wait - there's more! XD

if you can provide ans for 1 and 3 rd, it will very help full to me to continue my algorithm

just post what you want to do^^ If this violated company regularisation - just pick an exmple which is similar in concept.