Why are pictures imported with black around their edges?

I've seen numerous posts about it over the years and can't figure out... why this happens? If I have a white image on a white background there's no reason for a random black border to be imagined around it?

It goes away if I change the rescaling options but that can cause other footage to look like complete cr*p

Anyone know why this even happens? Attached an image just to show
It's easy enough to crop off 1 or 2 % I guess but it still shouldn't happen in the first place

It seems to me that the picture does not fit exactly the aspect ratio of the timeline. Have you tried to export the picture in the exact resolution of your timeline and import it in DaVinci Resolve?

Two possible reasons for this, just crappy alpha handling or resampling error (probably from filter with sharpening effect). My guess is on filter with sharpening. I can reproduce black lines on edges in Nuke with adding sharpening filter after transform. Regular transform does not do it, whatever the filter is, so I guess in Resolve they have something backwards in alpha and transform ordering.

It seems to me that the picture does not fit exactly the aspect ratio of the timeline. Have you tried to export the picture in the exact resolution of your timeline and import it in DaVinci Resolve?

I often use a lot of mismatched images so that don't fit in the aspect ratio, but it still shouldn't do this since it doesn't happen in Premiere

Two possible reasons for this, just crappy alpha handling or resampling error (probably from filter with sharpening effect). My guess is on filter with sharpening. I can reproduce black lines on edges in Nuke with adding sharpening filter after transform. Regular transform does not do it, whatever the filter is, so I guess in Resolve they have something backwards in alpha and transform ordering.

Seems to be something to do with the resampling definitely, hopefully it gets fixed in the future then!