How to properly configure the two image comparison (diff) function in node/node-red-contrib-image-tools?

How to properly configure the two image comparison (diff) function in node/node-red-contrib-image-tools? what you need to specify in the image2 input field when setting the path to the second image file. I did not find this instruction in the description of the node.

I can't remember if I added a diff option to image-tools but I did do a demo for someone: Compare to images , get simularity in percentage - #11 by Steve-Mcl