Image size reported as too small, but it's not

[nhoizey]

I don't know if it is the same issue as #29, but here's an example where the overlay tells me the image is too small, while it's not.

Here: https://nicolas-hoizey.com/2017/01/how-much-data-should-my-service-worker-put-upfront-in-the-offline-cache.html#webmention-419040

$('#webmention-419040 > article > div.webmention__source > a.u-url > img').currentSrc tells me the image is https://res.cloudinary.com/nho/image/fetch/c_fill,f_auto,q_auto,w_600,h_400/http://image.thum.io/get/width/1200/crop/800/noanimate/http://www.webhostingreviewsbynerds.com/web-development-reading-list-168-preload-with-webpack-a-guide-to-security-headers-and-service-worker-fallacies/

It is 600 pixels wide, and the CSS size in the page is 298 pixels, so on my 2x screen (MacBook Retina), it should be almost perfect.