Prefer screenshots using XCB over gnome-screenshot

docs/reference/ImageGrab.rst

@@ -15,8 +15,9 @@ or the clipboard to a PIL image memory.
     returned as an "RGBA" on macOS, or an "RGB" image otherwise.
     If the bounding box is omitted, the entire screen is copied.
 
-    On Linux, if ``xdisplay`` is ``None`` then ``gnome-screenshot`` will be used if it
-    is installed. To capture the default X11 display instead, pass ``xdisplay=""``.
+    On Linux, if ``xdisplay`` is ``None`` and the default X11 display does not return
+    a snapshot of the screen, ``gnome-screenshot`` will be used as fallback if it is
+    installed. To disable this behaviour, pass ``xdisplay=""`` instead.
 
     .. versionadded:: 1.1.3 (Windows), 3.0.0 (macOS), 7.1.0 (Linux)
 

src/PIL/ImageGrab.py

@@ -61,7 +61,17 @@
                 left, top, right, bottom = bbox
                 im = im.crop((left - x0, top - y0, right - x0, bottom - y0))
             return im
-        elif shutil.which("gnome-screenshot"):
+    try:
+        if not Image.core.HAVE_XCB:
+            msg = "Pillow was built without XCB support"
+            raise OSError(msg)
+        size, data = Image.core.grabscreen_x11(xdisplay)
+        im = Image.frombytes("RGB", size, data, "raw", "BGRX", size[0] * 4, 1)
+        if bbox:
+            im = im.crop(bbox)
+        return im
+    except OSError:
+        if xdisplay is None and shutil.which("gnome-screenshot"):
             fh, filepath = tempfile.mkstemp(".png")
             os.close(fh)
             subprocess.call(["gnome-screenshot", "-f", filepath])
@@ -73,15 +83,8 @@
                 im.close()
                 return im_cropped
             return im
-    # use xdisplay=None for default display on non-win32/macOS systems
-    if not Image.core.HAVE_XCB:
-        msg = "Pillow was built without XCB support"
-        raise OSError(msg)
-    size, data = Image.core.grabscreen_x11(xdisplay)
-    im = Image.frombytes("RGB", size, data, "raw", "BGRX", size[0] * 4, 1)
-    if bbox:
-        im = im.crop(bbox)
-    return im
+        else:
+            raise
 
 
 def grabclipboard():