different imagecache sizes on profile view

When creating a "latest visitors" block with the views module, the user avartars on the latest visitors block show up as big as the profile image on profile view. This is because all $user images on profile view get processed the same way eventhough the imagefield from "latest"visitors" was set to e.g. 50px instead of 150px which used by the profile image.

How can we have two different image sizes on profile view? One size e.g.150px for the default profile image and another block with user images who visited the profile with 50px image size.

Thanks for any hint.