http://www.imagemagick.org/RMagick/doc/image1.html

[nilab]

Magick::Image.readじゃStringIOは読めないのか。 "The read method does not accept a StringIO object. If you want to create an image from a string buffer, use from_blob." RMagick 2.12.0: class Image (class methods and instance methods a-d)