How to identify object(s) in image when given a list of all images?
Think of images as matrices (2D arrays) of numbers that indicate brightness. If you are looking for an exact match of an image in another, you are looking for comparing 2D integer arrays, which could be done with a double for loop that is done for each possible match location (so it is a 4 deep for loop acutaly).

A more interesting related problem is searching an image with no exact match, but with some kind of similarity instead. For that task you should read into template matching algorithms.