There is various open-source image creation and manipulation tools out there.
I suggest Inkscape and Gimp. In a terminal:
Code:
sudo apt-get install inkscape gimp
Inkscape creates svg graphics that can be scaled up and down infnitely. Resize these ones to the size required, then edit them in GIMP (it's like photoshop) Inkscape is fairly intuitive (as with gimp), but there's plenty of tutorials on the web if you're confused.