Create thumbnail of provided key, and save it as {key name}_medium.jpg

gistfile1.rb

# if "key" equals "bird.jpg", 
# then this code creates a smaller thumbnail of the bird, 
# sized to 270 by 167 pixels, 
# adding a watermark, 
# compressing the thumbnail to save space, 
# and saving the new thumbnail as "bird_medium.jpg"
Original.find(key).compress(70).resize(270, 167).to(:fit).watermark.save(:medium)