BitBlt Function question.

I was wondering, can you use the c++ BitBlt function to capture an image of a window (not your own window, but that of another program) then use a reference image to locate where on the image the reference image is.

I'm working on a bot program, and want it to be able to detect whether a button is labeled "a" or labeled "b" and then click it accordingly(the clicking part i already got solved)

is there a simple function that does OCR? i thought there were whole programs dedicated to that. so i thought It would be easier to have the program Analise a capture image pixel by pixel till it finds a match to the reference image... but I could be over thinking this.