This past year, I taught Computers at my son's school and I completed a couple "Silhouette" projects during the year with some of the classes. Since we did not have Photoshop software on the school computers, I used a great FREE photo editing website called www.ipiccy.com. It's truly awesome and has tons of great features!
Here are the directions that I gave my students to create their own silhouettes using iPiccy. Long, but simple.