I believe that 'blend' originally means a subtle mix of two (or more) things. This also goes well with the arty kind of blend that my site (and many other sites) are about. Most likely I'm no expert in this, but here I put a little explanation about the common styles of blends:

Pics
In Pics the pressure is on transforming two or more pictures seamlessly in one. Effects are also used to make the work seem more original and finished.
Add Effects
Also known as 'AE'. Quite similar to Pics, but the pictures are already together, and only the adding of effects -texts, brushes, textures- are important, pretty much as the name says.
Icon
From a full size picture to a 100x100px icon or 'avatar'. In here, effects are also used for a better blend.
Color
You are given a grayscaled image, which should be colored as well and as realistically as possible. In this one, effects can be used, but not as much as in the other styles. Too many effects will just distract, and most likely lead to a disqualification of some sort.
Retouch
The name of this style already says it pretty clearly: retouch the picture, so that the person in it looks more attractive.
Special
This isn't really much of a separate style, but in these the challenge could be anything. You might be asked to create a layout, a magazine cover or an authentic-looking tattoo.
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