How do you photoshop your friends pictures on Facebook?

[bravetrip458]

So I saw this really funny article online where these guys photoshopped their friends Facebook photos without their friend knowing it, and I have a friend doing it to me and I wanna pay them back! Does anyone know how to do these?

Heres the link: http://www.oliandalex.com/james-face/

Thanks!
Like, how do I edit their photos without them knowing?

[Rilakkuma]

With the color changes in the faces, all you really have to do is pick a specific part of the body and change the hue of the picture.