I get a lot of people asking me how do this and how to do that. So I decides to give out some handy tips which I use all the time!
These series of tutorals are for GIMP and most would apply to PSP, or Pro.
My main rule for making fanart is
experimenting!Dont be afraid to mess around with the colours, setting, and gradients.
I find most picture need to be lighten or contrasted. With Screencap I really need to lighten them but with professional shots and promo piccies I only need to lightly contrast.
So here we go
Step 1: Crop your picture

Especially with Avatars, crop them in a different way so that their face or the main object is not in center cause that looks boring and if you are going to add word you need space to write it.
Step 2: Scale to 100x100 and Lighten

For this step I copy the orginal layer and put the setting to "Screen" (this is a better way to lighten instead of adding a white layer on "Overlay"), Screen lighten with all the layers colours.
Step 3: Colouring and Contrasting through Dodge

I added a new layer and put it on "Dodge". I use Dodge alot becasue it not only lightens but it contrasts a bit too. It adds colours which makes it "glow" (as Edwina once told me).
This Dodge was a bit too much so I put the Opacity to " 10"
Step 4: Main Contrast

(Layer>Colour>Brightness and Contrast)
This picture was tricky it took me a few goes to get the contrast right. When I Contrast I usually put the contrast on more than the Brightness (it just looks better). With this picture I put the Brightness on 50 and the Contrast on 70
Step 5: Cream Layer

I used a cream layer on "Grain Merge" with the Opacity on 10 give his face more colour. You can put it on Overlay or Soft light too

Voila! The picture is ready to writen on!
Every picture is different, it all depends on the lighting and quality of the picture. So experiment and get a feel for the picture.
With dark picture you dont necessarily, need to lighten but definately contrast the light parts of the photo.
From this

to this

I did the exact same thing but I didnt use the Brightness and Contrast tool
I hope that was easy to understand. Next tutoral will be about Writing and Colouring!