Image site hits back at spammers
Spammers are being thwarted by finding that their junk messages unexpectedly contain warnings urging recipients to delete the e-mail.
The alerts are issued by ImageShack, in an effort to stop spammers using its services.
It is replacing pictures, known to have appeared in spam, with warnings such as "Do not buy".
Spammers often use image hosting sites so they can include fake logos, intended to make the mail look genuine.
The aim is raise users' awareness of the problem and to make life difficult for those sending the spam, Alexander Levin, president of ImageShack told BBC News.
"The net effect is that the spammers lose customers and see a decrease in revenue."Spam warning
ImageShack's system is capable of swapping thousands of the spammers' images for warnings within an hour of them being reported.
The company works with anti-spam groups to identify any files that have been uploaded to its servers and are being used in junk emails, he said.
It then scours its web logs to uncover other images that have been uploaded from the same web address.
This allows it to identify images "not previously reported to the anti-spam communities", Mr Levin added.
The move was welcomed by Paul Wood, senior analyst at security firm Symantec.cloud.
However, he warned that if image hosting sites are serious about tackling spam, they should consider their registration processes.
"Users often don't need to register to use these sites - making them highly disposable and open to abuse," he said.
According to security firm McAfee, the global volume of spam is at its lowest level since 2006.
That follows one of the largest group of spammers, known as Spamit, deciding to cease its activities last August.
Even so, spam accounts for nearly 80 per cent of all email traffic, McAfee reported.