gistfile1.rb

# Use ImageMagick to get the dimensions of an image
def get_image_dimensions(image_url)
  open(image_url, 'rb') do |f|
    @image = Magick::Image.from_blob(f.read)
  end
  "width=\"#{@image.first.columns}\" height=\"#{@image.first.rows}\""
end

# Insert the width and height into all img tags in a string
def insert_image_dimensions(string)
  string.scan(/<img (src="(.+?(\.gif|\.jpg|\.png))")(.*?>)/i).each do |result|
    dimensions = get_image_dimensions(result[1])
    string.sub!(result[0], '\0 ' + dimensions + '\3')
  end
  return string
end