This is best explained with images.
Firefox, right: 
Chrome, wrong: 
That is a (fully green) image with 2px (red) border and a border-radius of 6px. In my design, the border is barely visible, so the image looks completely square in Chrome.
Is it possible to achieve the correct result in Chrome without extra markup nor javascript?
I don’t believe you can do this with Chrome. Images will extend over the bounds of
border-radius, and I think that’s the intended behavior (or else they just didn’t notice).When using a
div, for example, you can see that the background behaves as it should. You could consider using adivinstead ofimg, and using your source image as the background (and forcing its width and height).Plainly said: In Chrome, there does not seem to be a way to force your image to be hidden by the border of itself (or even of its container) unless it is set as a background. In fact, the issue has been asked about before, and blogged about as well (and, in fact, patrickzdb‘s comment there may help you).