Compare the current screen with a saved screenshot

have a look at class Finder and the docs:
http://sikulix-2014.readthedocs.io/en/latest/finder.html#finder

HI RaiMan, thanks for the quick response,

I tried using finder and it did really solve my problem

I have 2 screen shots of 2 windows which have a lot of check boxes , I tried using the finder function for comparing them with a couple of check boxes checked in one screenshot and these check boxes left unchecked in the other; but the result was a match. To how much precision will the finder function find match for me? is there any other function which lets me compare screen to the level of a check box in the screen(or a small text box in the screen)?
I need to check if the two screens are exactly the same to the precision of a pixel(if possible)

to solve this, you have to check with an image of the checked and the unchecked situation against the checked and unchecked situation in the screenshot.

use match.getScore() to get the score value of each case.

then use these values (it is ok, to round to 2 decimals) and Pattern().similar() in the find ops.

depending on the concrete situation (scores), it might be necessary to check again with the opposite after a match.

In SikuliX version 1.1.1 a score >0.99 means exact match (depending on the size of the search image, some pixels might be different though (usually around edges)).
So due to the usage of the underlying OpenCV feature matchTemplate(), a precision of a pixel cannot be achieved: a match score only signals a very, very, very, ... high probability that the image matches the nearer the score gets to 1.000000000000...