Draw ignore-zone rectangles on the screenshot so Lemwatch masks noisy regions (ads, timestamps, carousels) before comparing pixels.
Open the monitored page, click Ignore Zones, and draw rectangles over noisy regions. Lemwatch masks those pixels black in both baseline and current screenshots before running the diff.
Site → Visual Monitoring → <page> → Ignore Zones.
Zones are pinned to CSS coordinates. Big layout changes may require redrawing.