There is a screenshots plugin, but the following @button script seems more useful

leo-screenshot.py

'''
This script must be bound to a keystroke so that it can run without disturbing Leo's present state. 
Rev 9cce9a in devel is required to make everything work smoothly when gathering arguments, but this 
rev breaks other features. Back to the drawing board.
-- @edreamleo, https://groups.google.com/d/msg/leo-editor/Serzpyzrylg/B63pKXFNCwAJ
'''
@button screen-shot @key=ctrl-1

'''
Create a screenshot of the present Leo outline and
save it to .leo/screen_captures.
'''
#  --window-size=682x1264 is recommended.
from leo.core.leoQt import isQt5, QtGui
import time
base = r'C:\Users\edreamleo\.leo\screen_captures'
assert g.os_path_exists(base), repr(base)
window = g.app.gui.qtApp.activeWindow()
w = window.grab() if isQt5 else QtGui.QPixmap.grabWindow(window.winID())
fn = '%s.png' % time.strftime('%Y-%m-%d-%H-%M-%S')
path = g.os_path_finalize_join(base, fn)
w.save(path, 'png')
g.es_print('saved: %s' % path)