[Koha] 404.pl

While watching the top command on my ubuntu server, I notice that while retrieving search items in the OPAC I get a lot of 404.pl instances. These seem to be a drag on the performance of the server. (We are a small school with a small VPS server). I assume that these are caused by Koha searching for missing covers. Is there any way to mitigate the effect of these searches? Is there a timeout setting or even disable these searches? Thanks.