Command line tool. This create a sample image.
$ brew tap nomuyoshi/sampleimage
$ brew install sampleimage
$ sampleimage --help
$ sampleimage ./sample1.png
$ sampleimage ./sample2.jpeg --width=500 --height=500
$ sampleimage ./sample3.jpg --W=400 -H=400 --bg=green
$ sampleimage ./sample3.jpg --W=400 -H=400 --bg=green --text='Sample thumbnail!!'