That's tricky on a responsive site. I'm not sure what happens if you enter dimensions larger than the container itself.

Why not just make the mages max-width:100%?

I'm pretty sure they are

We'd need some way to get the intended size + ratio of every image requested on the page, before they actually finish loading. We wouldn't be able to do that for a server that's down so it wouldn't work for what we need anyway

oh wait I didn't read all of the replies. we're talking about something else nvm