Translate a thumbnail into a rounded thumbnail. Basically this: http://stackoverflow.com/questions/11233887/cut-circle-out-of-image-with-rmagick but this implementation wasn't working as expected. Instead of a rounded image, i would receive an image with a miscellaneous black circle in the corner.

thumbnail.rb

# System command. 
# convert original.image.png -resize '168x168^' -gravity center -crop '168x168+0+0' original.resize.png; 
# convert -size 168x168 xc: -fill original.resize.png -draw 'circle 75,75 25,1' thumbnail.png