Now I’d argue that the display was acceptable. I agree that it’s not a perfect solution but I don’t think you can ask for more. The theme is going to have to deal with users who may have moved from a 1000px content area to your 620px content area. Something is going to have to “give” if they’ve inserted whacking great images onto the page.
The only other option might be use overflow:hidden;
. That won’t skew the large images but it will hide part of them. At the end of the day, your job is to try & ensure that the design doesn’t break in these conditions – which it doesn’t. The content is down to the site owners/authors. They can either resize the images to suit, live with your “fix” or use another theme. You’ll never satisfy everyone all of the time but what you have done is to comply with that criteria in the Theme Review.