If you will go to this address: http://www.slate.com/id/2154271/?GT1=8805, you should see an article called The Curious Economics of Temptation. It's from Slate, that online magazine one finds (only, I think) on MSN.com.
Now let's say you copy-paste the entire article into Word, along with the picture in the article of the sexy girl. And let's say further that you really didn't want the picture of the sexy girl but had no easy way to copy the artile without the girl because you could not highlight only the article.
However Word will let you remove the picture of the sexy girl from your copy- paste action. (You need to click on a small icon in this instance near the lower left corner of the picture.) When you do that, the picture immediately changes color dramatically and looks like a film negative (or a color film negative). At this point you can go edit > cut and the picture vanishes from your Word document.
OK. what happens or has happened in the process of creating/copying the image that causes it to look like a negative when I click on those tiny icons. (The icons are tiny yellow things about 1/4" x 3/8".)