Well, yes.   Sort of.  Using a Rich Text field.

Do a screen grab using whatever method for your particular platform, and then just copy and paste into the field.

For example, if you're using a Windows PC (web version of Ninox) go to the screen you want to capture and press 'Fn+Print Screen' to copy the whole screen and then Ctrl+V in the Rich Text field.  Alternatively, use the Windows Snip & Sketch utility to just capture a portion of the whole screen, then do a Ctrl+C to copy the image and Ctrl+V to paste into the Rich Text field.

Mac, Android, and iOS all have there own ways of copying (and cropping) a screen and pasting, but the key is to use a Rich Text field.  I don't think you can use an Image field without first saving as a file/image.