You mind using texplay? Here's a quick example:

require 'gosu'
require 'texplay'
include Gosu

class MyApp < Window
  def initialize
    super 200, 200, false
    @image = Image.new(self, "heart.png", true)
    @x = 10 # @image pos x
    @y = 10 # @image pos y
  end
 
  def needs_cursor?
    true
  end
 
  def update
    if button_down? MsLeft and (@x..@x+@image.width).include?(mouse_x) and (@y..@y+@image.height).include?(mouse_y)
      puts "clicked" if @image.get_pixel(mouse_x - @x, mouse_y - @y)[3] != 0.0
    end
  end
 
  def draw
    @image.draw(@x, @y, 1)
  end
end

MyApp.new.show

Just replace heart.png with your image of choice! Ask if anything isn't clear in this code.

You can also use Image#to_blob, which returns a binary string (and cache it), and then index into that -> image_blob[width * y + h]. That will then return an argb string. Not pretty, but 0ldsk00l.