To review your users' (or your own) screen shots, you can go to Track Time tab at the top navigation. On Track Time page, you see the a table of thumbnail images that are displayed based on the time line that the screen shots are logged. You might want to look at the full-size image of the screen shots and drill in the details. You can click the magnifier icon to the left of a thumbnail image to bring up the Screenshot Viewer to view the full-size image and the detailed information associated with the thumbnail. 

With the Screenshot Viewer, you can easily navigate the screen shots by moving forward or backward for the next or previous image. For each screen shot, you can zoom in/out either by using the buttons or by using your mouse scroll wheel. You can use mouse to grab the image to pan it (when the image is enlarged and overflows the viewer). On the right-hand side, the information for the time slot (such as task, user entered description, activity meter) is displayed, as well as the detailed activity history. You can also adjust size the default image panel to suit your viewing comfort. If you select the largest size, the screen will fill the whole page and the right information panel will be suppressed, which is handy if you wish to see only the screen shot image.

The following is a diagram that explains various functions on the screen shot viewer.

(Click here to enlarge the image)