open(IMAGE, 'image.gif') opens a real file using the OS services but IO::Scalar objects exists only inside perl.

You can see the difference using the fileno() builtin: 

open IMAGE, "image.gif";
printf "fn: %d\n", fileno(IMAGE);

my $ios = IO::Scalar->new;
printf "fn: %d\n", fileno($ios);

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In reply to Re^4: reading image blob w/Image::Magick by salva
in thread reading image blob w/Image::Magick by yoz-y

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