Screenshots not 144 pip instead of 72 pip. NOT good for me.

I constantly took screenshot to modify online imagery which is 72 ppi source imagery. 72 ppi screenshots were pixel to pixel copies of the art do I could re-publish it. 144 is not! It is interprolate images (which is awsome for viewing 72 ppi on the high density screens) How can take 72 ppi screen shots now?

Simple senario. Client asks to modify something on thier site. I take a screenshot of the entire site and use that as the base art of modificaiton which I can then just re-slice or provide to them to use. Now my image is not usable.

Please advise on how to capture pixel to pixel screen capture.

Thanks!