Is it possible to make it mandatory that each closed work order has attachments before it can be closed?


This feature exists in ServiceBox.  If you go to : Settings - > Work Order -> Close Workorder Setup.  There is an option there called "Minimum number of attached images before closing workorder", if you want to have 1 image required enter one.  


What this will do is, once the Work Order is closed it will check to see if there has been 1 attachment added.  If there is one then the Work Order will close.  If there isn't then the Work Order will not be set to closed, the user will get a message that a certain # of attachments is required.  The user will then need to add an attachment into the Work Order.


You can make any number of attachments mandatory and then this number of attachments must be included before you can close the  Work Order.