KM 8.2.4 on macOS 10.13.6 here. For some reason, your test macro wouldn't find the image either in the main screen or front window for me, but once I replaced it with an identical one screenshotted on my own system (this one, for what it's worth:
both actions succeeded for me just fine in both Safari 12.0 and the official 64-bit build of Chrome 69.0.3497.100.
You don't specify which browser you're running here, but in this thread (Found Images suddenly broken) you said it occurred while running Chrome 69.0.3497.100 (3497.100); did you also try it with Safari? If it is only in Chrome, it's almost certainly a problem with Chrome no longer reporting window (and tab) indexes or IDs correctly as of the most recent versions, and not with KM. @ccstone and I discussed this a bit here, and it seems that even though Chrome is at least reporting window indexes correctly in the official build as of 69.0.3497.100, it still doesn't resolve the issues with KM actions that involve looking for the front window, at least on macOS Sierra.