Thank you for your fast answer.

With your information about the HTML* parser, I changed the 
DefaultContents to TXT. swish-e is now several times faster. But I get 
now for each Image a warning. Do you know how I can suppress these 
warnings and is there any limitation if I'm using TXT for the 
DefaultContent-Scanner, when I will set all other scanable files to 
another scan engine?


Warning: Substituted 677 embedded null character(s) in file 
'/var/samba/daten/dokumentationen/mozillamailer/pfeile.bmp' with a newline

Thomas