A guide to making silhouettes with GIMP (By Ketsu):
PART 1: Making a silhouette with Gimp.
Start out with a render or a drawn picture, with a white background. If your selected picture has a black background, that's fine as long as the character looks bright against the blackness.J ust go to Colors -> Invert to reverse it to blackened character. For this part of the guide, I have chosen Sanosuke Sagara from Rurouni Kenshin.
Select Colors -> Threshold...
Make sure the "Preview" check box is selected. Then, adjust the black and white arrows until the background is as white and clean as possible without any dots anywhere around the character in the picture. (The dots aren't a problem, but it's annoying to have to clean them up later.)
When you get to good point on the threshold, click OK. If there are still any areas on the character that are not outlined in black and are connected to the white background, close it up with black as best as you can.
Now, select the Bucket Fill option and start filling in white areas in the character. Switch to the paint brush for the white/gray dots scattered here and there. Clean up any unwanted dots. Now go to File->Save as... Now Name the file, select your destination path, and drop down the "+ Select File Type (By Extension)" menu. Select your extension, and save it. If you get a message saying something like "JPEG Plug-in can't handle Transparency", select "Export" and then "Save".