As of Smartsite 7.10, the Media Library also supports the Bulk update action.
Just select two or more images and select the Bulk update button (you need to click the drop-down button first).
The Bulk update action will open in a new tab and will display an overview of the selected items and the current values of the fields for which the ctfp bulkupdatable is set to true.
The Title field is always included as information, it usually will not be bulkupdatable.
Select the fields you want to set using Bulk update. The Bulk update action uses the same tab lay-out as Edit Item does, but with every field initially set to hidden. When selecting one or more fields, the field(s) will be set visible, so one or more tabs will become available.
Notice the edit controls for the selected field(s) will be empty, since the selected items can have different values for the field(s).
Fill in / select the value(s) you want to set for the selected items and click the Save button.