Screenshots are actually generated by alarms. The alarm criteria are evaluated every time there is a change in the active window titlebar. The default screenshot alarm is set to take a screenshot 20 seconds after a change in the active window titlebar, unless it is preempted by another change.
The free version of the product only allows one screenshot for each change in the active window titlebar. The paid version allows multiple/continuous screenshots at a configurable time interval.
Screenshots and alarms in general can be targeted at specific types of activities. Alarms can be set to trigger based on any column in the Activity Log. (The Activity Log keeps a running record of all active window titles and associated data.)