Try this: http://www.phatcode.net/downloads.php?id=194

You can use a screen grabber application for than, like in early windows before the alt+printscreen.
But of course because it's DOS, it'll stay in memory as a TSR and will be triggered with some key combination to take the screenshot.
I mostly use "Screen Thief" (really easy to find, just google something like "screen thief" and "dos" or "capture" and it'll appear in the first page) but there are literally dozens of them.

I can't help a personal comment here as these applications seem to hate me. Whenever I really, really want to capture something they never work. Some don't work on a 8088, some don't capture from a Hercules adapter, some games block the "hotkey" and so on...

Edit: that's funny, the above link posted as I was writing leads to Screen Thief!

Thanks, looks like what I needed.

konc wrote:

I can't help a personal comment here as these applications seem to hate me. Whenever I really, really want to capture something they never work. Some don't work on a 8088, some don't capture from a Hercules adapter, some games block the "hotkey" and so on...

Hercules is somewhat tricky since there is no official way to detect if the card is in text (MDA) or in graphics mode.
The unofficial trick I read about is to count retrace lines - 350 means text mode, 348 graphics mode.