This tutorial uses GIMP - GNU Image Manipulation Program. It is a free and open-source graphics editor.
1. Find an image to use as the template for the silhouette and open in GIMP
2. Crop image to area of interest
3. Convert image to a reduced color palette
Select Image -> Mode -> Indexed…
The indexed image mode will limit the color palette to a limited number of colors. Select the maximum number of colors to use for the color map. The lower the number the better, but make sure that there is not too much detail lost.
Note: you may need to convert the image back to RBG mode in order to complete the next few steps.
4. Select the background using the Fuzzy Select Tool
5. Delete the selection
First make sure that the image has an Alpha channel.
Select Edit -> Clear
Then, use the Eraser tool to clean up any remaining background areas
6. Covert image to reduced color palette with fewer colors
Indexed image with few colors (max 2 or 3) and fill selections (Select by Color Tool) to match color schema
7. Scale and center image
8. Export image as a .png