In fast moving environment it is possible that disk images (.gho or .img) are created and used for a short period of time.
However based on the nature of those disk images they can take up a lot of space on the Symantec Management Platform server and on Package Server, and deleting them can be tricky (leaving orphaned items on the DB or files on the SMP / PS's).
DS 7.x, 8.x
The following steps are recommended to ensure the disk images that are no longer needed are first delete from disks (on the SMP and PS's) and then deleted form the Database:
Locate the disk image you want to remove on the Symantec Management Console. You want to keep a copy of the Image Resource guid  and of the Disk Image package 
Extracts the package folder from the "Disk Images" package 
Cleanup the package source i.e. remove all files from the package to ensure no traces (Important Note! You may want to take a back up of the image files or double check that you are not removing an image that is still in use before completing this step and the next one)
Run the package distribution point update task
Delete the Image Resource  from the Management Console
The following SQL query can be used to track the cleanup process of the package servers (please make sure you use a specific package name instead of the generic %.gho filter highlighted in yellow below) :
select p.Name, p.[Package Location], p.[Package Size], p._Refreshed, p.Version, s.Version, s.Status, s.IntStatus, i.Name, i.Domain, i.[OS Name] from SWDPackage p left join SWDPackageServer s on p.PackageId = s.packageid left join Inv_AeX_AC_Identification i on s.PkgSvrId = i._ResourceGuid where p.Name like '%.GHO' and p._Latest = 1