Launch the Visual Policy Manager. Go to Configuration> Policy >Visual Policy Manager.
Create a Web Access layer, and the Destination field select Combined destination object.
Click Edit.
Click New >Request URL. Under regular expression enter tbm=vid to block videos andclick Add, then enter tbm=isch to block images and click add. Both the Request URL regexes will display on teh left pane.
Add both Request URL objects you created in the combined destination object .