diff --git a/ucs-school-4.1/ucs-school-umc-computerroom/debian/ucs-school-umc-computerroom.univention-config-registry-variables b/ucs-school-4.1/ucs-school-umc-computerroom/debian/ucs-school-umc-computerroom.univention-config-registry-variables
index 4d62e40..51b9836 100644
--- a/ucs-school-4.1/ucs-school-umc-computerroom/debian/ucs-school-umc-computerroom.univention-config-registry-variables
+++ b/ucs-school-4.1/ucs-school-umc-computerroom/debian/ucs-school-umc-computerroom.univention-config-registry-variables
@@ -9,3 +9,15 @@ Description[de]=UMC-Computerraum-Administration: auf "yes" setzen, um UltraVNC-S
 Description[en]=UMC-Computerroom-Administration: set "yes" to activate UltraVNC shortcut (Default: false)
 Type=str
 Categories=management-umc
+
+[ucsschool/umc/computerroom/hide_screenshots/groups]
+Description[de]=Kommaseparierte Liste mit Gruppennamen, für deren Mitglieder keine Screenshots im Computerraum-Modul angezeigt werden sollen (Standard: Domain Admins)
+Description[en]=Comma separated list of group names, for whose group members no screenshots are shown in computer room module (Default: Domain Admins)
+Type=str
+Categories=management-umc
+
+[ucsschool/umc/computerroom/hide_screenshots/teachers]
+Description[de]=Der Wert "true" verhindert die Anzeige von Screenshots von Lehrer-Rechnern im Computerraum-Modul (Standard: false)
+Description[en]=By setting this variable to "true", screenshots of teacher's computers are not shown in computer room module (Default: false)
+Type=bool
+Categories=management-umc
diff --git a/ucs-school-4.1/ucs-school-umc-computerroom/umc/python/computerroom/__init__.py b/ucs-school-4.1/ucs-school-umc-computerroom/umc/python/computerroom/__init__.py
index be76005..029f5c1 100644
--- a/ucs-school-4.1/ucs-school-umc-computerroom/umc/python/computerroom/__init__.py
+++ b/ucs-school-4.1/ucs-school-umc-computerroom/umc/python/computerroom/__init__.py
@@ -81,7 +81,8 @@ from notifier.nf_qt import _exit
 _ = Translation('ucs-school-umc-computerroom').translate
 
 ROOMDIR = '/var/cache/ucs-school-umc-computerroom'
-
+FN_SCREENSHOT_DENIED = '/usr/share/ucs-school-umc-computerroom/screenshot_denied.jpg'
+FN_SCREENSHOT_NOTREADY = '/usr/share/ucs-school-umc-computerroom/screenshot_notready.jpg'
 
 def _getRoomFile(roomDN):
 	if roomDN.startswith('cn='):
@@ -545,17 +546,27 @@ class Instance(SchoolBaseModule):
 		"""
 
 		tmpfile = computer.screenshot
-		if tmpfile is None:
-			# vnc has not (yet) received any screenshots from the computer
-			# dont worry, try again later
-			self.finished(request.id, None)
-			return
+		if computer.hide_screenshot:
+			filename = FN_SCREENSHOT_DENIED
+		elif tmpfile is None:
+			filename = FN_SCREENSHOT_NOTREADY
+		else:
+			filename = tmpfile.name
+
 		response = Response(mime_type = MIMETYPE_JPEG)
 		response.id = request.id
 		response.command = 'COMMAND'
-		with open(tmpfile.name, 'rb') as fd:
-			response.body = fd.read()
-		os.unlink(tmpfile.name)
+		MODULE.info('screenshot(%s): hide screenshot = %r' % (computer.name, computer.hide_screenshot))
+		try:
+			with open(filename, 'rb') as fd:
+				response.body = fd.read()
+		except (IOError, OSError) as ex:
+			MODULE.error('Unable to load screenshot file %r: %s' % (filename, ex))
+		try:
+			if tmpfile:
+				os.unlink(tmpfile.name)
+		except (IOError, OSError) as ex:
+			MODULE.error('Unable to remove temporary screenshot file %r: %s' % (tmpfile.name, ex))
 		self.finished(request.id, response)
 
 	@check_room_access
diff --git a/ucs-school-4.1/ucs-school-umc-computerroom/umc/python/computerroom/italc2.py b/ucs-school-4.1/ucs-school-umc-computerroom/umc/python/computerroom/italc2.py
index b45a33c..564c437 100644
--- a/ucs-school-4.1/ucs-school-umc-computerroom/umc/python/computerroom/italc2.py
+++ b/ucs-school-4.1/ucs-school-umc-computerroom/umc/python/computerroom/italc2.py
@@ -115,13 +115,22 @@ class UserMap( dict ):
 			MODULE.info( 'Unknown user "%s"' % username )
 			dict.__setitem__( self, userstr, UserInfo( '', '' ) )
 		else:
+			result[0].open()
 			userobj = UserInfo( result[ 0 ].dn, username )
-			for grp in result[ 0 ][ 'groups' ]:
-				if grp.endswith( search_base.workgroups ):
-					userobj.workgroups.append( udm_uldap.explodeDn( grp, True )[ 0 ] )
-				elif grp.endswith( search_base.classes ):
-					userobj.school_class = udm_uldap.explodeDn( grp, True )[ 0 ]
 			userobj.isTeacher = search_base.isTeacher( userobj.dn )
+
+			blacklisted_groups = set([x.strip().lower() for x in ucr.get('ucsschool/umc/computerroom/hide_screenshots/groups', 'Domain Admins').split(',')])
+			users_groupmemberships = set([udm_uldap.explodeDn(x, True)[0].lower() for x in result[0]['groups']])
+			MODULE.info('UserMap: %s: hide screenshots for following groups: %s' % (username, blacklisted_groups,))
+			MODULE.info('UserMap: %s: user is member of following groups: %s' % (username, users_groupmemberships,))
+			userobj.hide_screenshot = bool(blacklisted_groups & users_groupmemberships)
+
+			if ucr.is_true('ucsschool/umc/computerroom/hide_screenshots/teachers', False) and userobj.isTeacher:
+				MODULE.info('UserMap: %s: is teacher hiding screenshot' % (username,))
+				userobj.hide_screenshot = True
+
+			MODULE.info('UserMap: %s: hide_screenshot=%r' % (username, userobj.hide_screenshot))
+
 			dict.__setitem__( self, userstr, userobj )
 
 _usermap = UserMap()
@@ -383,6 +392,14 @@ class ITALC_Computer( notifier.signals.Provider, QObject ):
 		return (self._computer.info.get('mac') or [''])[ 0 ]
 
 	@property
+	def hide_screenshot(self):
+		global _usermap
+		try:
+			return _usermap[str(self._username.current)].hide_screenshot
+		except AttributeError:
+			return False
+
+	@property
 	def isTeacher( self ):
 		global _usermap
 		try: