Finding a suitable way to compare images in java

Hey all,

Ive been hunting around the net for a suitable way to compare two images. Ive come across quite a few answers but none are as plain as i had hoped.....

The plan is, in the end, make a game where i can play with friends over internet. But the catch is i want to have webcams set up on the playing field and i want the cam to be able to detect which cards are played. Im pretty sure i want to compare images, well at least start at comparing images and check wether or not they are the same.

Could someone please point me in the right direction of comparing images as i am alittle lost...

Thanks in advance!!