Most internet browsers allow you to prevent pictures from being downloaded on a site by site basis. If you can't see any profile pictures, but can see pictures such as the Site's Logo and other navigation elements, then the chances are you've blocked images from being loaded in your browser.
In Firefox you can manage the blocked image settings by typing in 'about:config' into the address bar at the top and searching for 'permissions.default.image'. If the value of this entry is anything other than '1', you should right-click the entry and select 'Modify', then change the value to 1.
Other Internet Security programs may also provide this blocking facility and the settings in each should be checked to ensure images are permitted to load.