In order to use the mass operation to print multiple images in Relativity you need to be using the ActiveX viewer. Relativity 9.0 and higher use Oracle's HTML5 viewer by default. You can install the ActiveX viewer under the Administration parent tab, and the Workspace Details child tab. In the Relativity Utilities section to the right you will see the option to download the Viewer Installation Kit. After installing it you will need to restart your web browser.
Confirm that you are set for the ActiveX viewer by going to the Instance Settings tab in your environment and then filter for the UseLegacyViewer setting. Set the value to true.
You can set the viewer a user uses by default under User and Group Management. . . User.