I have recently found out about it, and it's much faster than ffmpeg, maim, scrot, and [shot](https://github.com/rr-/shot).
With [an image like this](https://0x0.st/i2N-.png)
- ffmpeg takes `0.349` seconds
- maim takes `0.970` seconds
- scrot takes `0.338` seconds
- shot takes `0.844` seconds
- shotgun takes `0.259` seconds.
and with an image [like this](https://0x0.st/i2NH.png) (200x200+1440+0 geometry)
- ffmpeg takes `0.747` seconds
- maim takes `0.018` seconds
- scrot doesn't allow you to provide a custom geometry, so I can't do a fair test (Also, when using the selection option it sometimes leaves white lines in the screenshot)
- shot takes `0.063` seconds
- shotgun takes `0.018` seconds
I personally use [crud](https://github.com/ix/crud) for making a selection.