profile_image_url - This is a direct link to the most up to date image that CrunchBase has at the time that REST API call is made or the data export is generated.
logo_url - This is a link that will always redirect to the most up to date
profile_image_url that CrunchBase has for a given entity. This link is only available in the Daily CSV Export.
Beginning with this image from the CrunchBase profile:
You could resize the image to a 40x40 pixel square.