[MTxHaloReach]

This will only work if the render you want to use has a flat color behind it. This is great if you dont want ot have to do all that cutting out! Lets get started!
Spoiler (Click to View) [IMG]http://i1118.photobucket.com/albums/k614/Isaac_Newsum/tutscreen1.png[/IMG]
Start By opening Your Render you want to use like this. See how theres that black box? we are going to get rid of that perfectly.
[IMG]http://i1118.photobucket.com/albums/k614/Isaac_Newsum/tutscreen2.png[/IMG]
Then you want to go to Colors>Color To Alpha and that screen should pop up. make sure you have your render layer selected. Then change the color to the color you wan to get rid of. in my case the background of the render was black so i made the color black. If the color you want gone is white change it to white ect..
[IMG]http://i1118.photobucket.com/albums/k614/Isaac_Newsum/tutscreen3.png[/IMG]
After youve done the previos step you should get this. not quite what we want but if you fill the back ground in wth black it will be good as new! This works great on smoke that would normally be impossible to get off the white background.

[IMG]http://i1118.photobucket.com/albums/k614/Isaac_Newsum/tutscreen4.png[/IMG]
And thats the finished product! as you can see i can draw around the render with out going underneath the black bax around it like there was!
Hope this helped!
Please dont copy my tutorial

[Nostre]

Seems like a great tutorial. I just viewed through it. But the pictures seem great and easy to explain.

[cybr]

Technically it's already rendered, just with a black background.

[DaZee™]

If It has A Black background for photoshop, Select --> Colour Range --> Click Black --> Delete (Obviously the black on your render(If there is any) will be deleted though...)

[MTxHaloReach]

If It has A Black background for photoshop, Select --> Colour Range --> Click Black --> Delete (Obviously the black on your render(If there is any) will be deleted though...)

thank you for that. i forgot about doing it on photoshop.

[DaZee™]

thank you for that. i forgot about doing it on photoshop.

No problem, I'm gonna be in this section a LOT more :)