Again “a bit late” and does only work in some cases (probably not in the OP case) but another solution would probably be using another rounded border to hide some of the content, so it gives the appearence that is rounded, without being rounded (here in the case of an image, we would put a border over the image). The caveat is it -only- works to make visual consistence, but still the image doesn’t have to go to the masked zone of the background image.
Here a conceptual graphic (havn’t applied it but I think it shoud work). 1 shows the image over the rounded background, 2 shows the border over the image, with the border colored for clarifying porposes. 3 would be the final effect.
Of course the border has to be thick enough, because if not you’d see the corners and the “faked” effect would be ruined.
