I guess the problem here is that ImageMagick is installed as a build tool on the development environment (DEV@cloud) but not on the stack you are using for the runtime environment (RUN@cloud). I cannot see any ImageMagick dependency added into the Tomcat 6-7 stack.
Only way to have imagemagick on runtime is to create a specific new stack which makes it available for you. So need to fork the git repo and use genapp as a development tool for the new stack.