Wikimedia Bugzilla is closed!

To provide sharp images to (most notably) mobile devices, especially newer ones with high-DPI, I suggest utilizing their physical / device pixels by offering overly-sized images comparing to "displayed" size.

For example, for device-pixel-ratio:2 devices (e.g. iPhone 4, Galaxy Nexus, new iPad), an image to be displayed in 300px×225px (measured in virtual pixels) should be provided with one originally sized 600px×450px (measured in physical pixels). Apart from device-pixel-ratio:2 there are also devices with ratio 1.5.

I see this is technically possible in Wikipedia for many thumbnail images, since many raster images have their original size more than quadruple of their thumbnail size, and many other images are simply vector. And it is left whether the rendering engine can determine the best image resolution, either by client side CSS or on server side.

Mobile browsers with webkit engine (Android browser, Safari, Chrome), Firefox and Opera has already added device-pixel-ratio media filter in CSS3. While Internet Explorer mobile for Windows Phone does not seem to support yet, fallback to current resolution is still possible.

While this does not provide more information regarding the subject most of the time, it still lets those devices show clearer and more detailed photos with their full display capabilities. This can be important for diagrams shown on such tiny screens.