Auto Screen Capture is a small and lightweight freeware for Windows which can capture screenshots for up to 4 displays. Also, this process of capturing screenshots can be automated and can be scheduled at specific time intervals if needed.

Download and install Auto Screen Capture from here.

The main interface shows the windows for all displays as well as specific settings for capturing screenshots.

The screenshots can be stored at specific locations and can be  saved in any of the common image formats like BMP, EMF, GIF, JPEG, PNG, TIFF, or WMF.

To automate screen capture at regular time intervals (e.g : a screenshot of the active window at every 15 minutes), click on Screen Capture tab and change the time settings. Also, a limit to how many screenshots can be taken during that interval can be set too.

Click on Start Capture button to capture screenshots.

To specify if the screenshots are to be taken continuously within a time range or only on specific days, scroll down to Schedule tab and change settings as needed.

The calendar will show the dates when screenshots were taken.

Also, keystrokes during screenshots can be logged to a file and image editors can be added for the captured screenshots.

This is a very useful screenshot tool with many features and is a freeware. Do give it a try.