Spam with only an image?

[Max Kipness]

I had just lowered the score on a domain complaining about spam to 5,
yet when checking some of the spam that got through, I noticed that most
of them have a score lower than 5 and just consist of an image with
maybe a line of text at the bottom.
 
Does anybody have a way to stop these? Seems like an easy way for a
spammer to get through.
 
Max
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