<%

my_file = File.open("image.jpg", "rb") {|f| f.read}
img = ImageSize.new( my_file )


# Testing: get img width with image_size lib.

img_witdh = img.get_width

%>

If you get "JPEG marker not found!" error when you try to open an image file you must read it in binary mode.

Avoid "JPEG marker not found!" error

file, error, ruby

Ruby