[anthk]

pledge(4)ing an image or video viewer under OpenBSD doesn't look difficult at all.

Also, you can convert your PNG images to Farbleld (+.gz | +.xz) without losing quality.

And the farbleld image format it's more difficult to exploit.

[geofft]

I think running pledge(2) on Windows is quite difficult. :)

(At least, I'm assuming the question here is "What should Windows Defender do?" I agree that the answer to "What should OpenBSD's built-in antivirus do?" is "Literally not even exist," which it already does.)