That would be the screen produced by this code in Screens/Standby.py.
Code:
class QuitMainloopScreen(Screen):
def __init__(self, session, retvalue=1):
self.skin = """<screen name="QuitMainloopScreen" position="fill" flags="wfNoBorder">
<ePixmap pixmap="icons/input_info.png" position="c-27,c-60" size="53,53" alphatest="on" />
<widget name="text" position="center,c+5" size="720,100" font="Regular;22" halign="center" />
</screen>"""
Screen.__init__(self, session)
from Components.Label import Label
text = { 1: _("Your %s %s is shutting down") % (getMachineBrand(), getMachineName()),
2: _("Your %s %s is rebooting") % (getMachineBrand(), getMachineName()),
3: _("The user interface of your %s %s is restarting") % (getMachineBrand(), getMachineName()),
4: _("Your frontprocessor will be upgraded\nPlease wait until your %s %s reboots\nThis may take a few minutes") % (getMachineBrand(), getMachineName()),
5: _("The user interface of your %s %s is restarting\ndue to an error in mytest.py") % (getMachineBrand(), getMachineName()),
42: _("Upgrade in progress\nPlease wait until your %s %s reboots\nThis may take a few minutes") % (getMachineBrand(), getMachineName()),
43: _("Reflash in progress\nPlease wait until your %s %s reboots\nThis may take a few minutes") % (getMachineBrand(), getMachineName()) }.get(retvalue)
self["text"] = Label(text)
It's not an image from a static file.