[jeremy_wiebe]

Is it not due to the inexactness of mapping the image pixels to device pixels? (Similar to what happens when drawing text with antialiasing)?

[kroltan]

In principle it could be, but usually browsers snap element rectangles to the pixel, thus protecting against that (have you ever seen a blurry border on a box because its contents had 0.5px size? nope, even though it is annoyingly common in things such as game UIs)

Plus you can see the same effect on the UFO tests, which strictly uses integer positions so pixel misalignment is not a factor.