Couple suggestions:

  def ImageBlob.inject_attrib_assign_methods

to

  def self.inject_accessors

Using 'self' is more robust. Also in Ruby attribute methods are
generally refered to as accessors.

  def ImageBlob.getBlob( file, max_image_size )
    begin
      img = Image.from_blob( file.read ).first
      if not img
        raise
      end

to

  def self.get_blob( file, max_image_size )
    begin
      img = Image.from_blob( file.read ).first
      return nil if not img

Don't use camelcase (unless you're passionate about it) and there's no
need to raise if the rescue clause is just going ot return nil anyway.

T.