Most of the time they can, but there are plenty of edge cases where it's difficult to tell apart. If you see enough Japanese, Chinese, and Korean people, even as a white person you'll develop a knack for telling them apart most of the time by facial features alone.

Source: I speak Japanese and this topic has come up many times with my Japanese coworkers. I can tell pretty well myself at this point too.

Most of the time they can, but there are plenty of edge cases where it's difficult to tell apart. If you see enough Japanese, Chinese, and Korean people, even as a white person you'll develop a knack for telling them apart most of the time by facial features alone.

Source: I speak Japanese and this topic has come up many times with my Japanese coworkers.