Support HiDPI (Retina Display) images displaying it in their "correct" display size
When including retina display images, it will get displayed, many times more, the difference between Browsers DPI (72) and images own DPI. For Apple Retina Display images, DPI is 144 so image is twice as big. If you take from mobile devices this can be even bigger.
When you attach a retina display image to GitHub it resizes the
img tag taking the DPI in consideration. So if the PNG file was 1000x500 and 144 DPI, the
img tag will be 500x250.
The only way to specify that in Markdown is to not use markdown, and fallback to HTML tags, which is what they are using.
When we receive the image on the backend, we can read the exif and retrieve DPI information. With that information we can decide how it will be displayed. It will either be generating a custom img tag with calculated width/height or a custom change to Markdown to support custom sizes.