divided by 0 (ZeroDivisionError)

/home/harunaru/tdiary/image-gallery.rb:152:in `/'
/home/harunaru/tdiary/image-gallery.rb:152:in `make_image_data'
/home/harunaru/tdiary/image-gallery.rb:58:in `initialize'
/home/harunaru/tdiary/image-gallery.rb:489:in `new'
/home/harunaru/tdiary/image-gallery.rb:489
image-gallery.rb:2:in `require'
image-gallery.rb:2