Spam that is nothing but one large image

[Matt]

Hi,
We have received a large quantity of spam that is nothing but a large
image.  Spamassassin is tagging it a little because it is an image,
and only an image, however I'm wondering how other people are
handeling this type of spam?    I don't want to score mail that is
just an image with a very high score, since that could render a legit
mail with a picture in it or something as spam.  Any thoughts?