Basically you find an image of a logo, then you cut it up to reveal a section of it that allows you to guess what the image used to be (easily done in paint

Here's an example....
NB: I spoiler tagged the answer so people can guess if they want to



Here's the first image

It's a pretty famous logo, so yeah, first one to guess correctly gets a cookie.
PS: If you need somewhere free easy and simple to upload, without registration, go here... http://imageshack.us/