To support high-density displays, we generate or fetch media thumbnails at three resolutions: standard 1x, 1.5x, and 2.0x density.
When going over InstantCommons, this currently requires us to make three separate thumbnail lookups over the internet, which are done in serial and can product quite some latency.
(For the more general issue that each image is looked up separately during parsing, see bug 54033.)
If the imageinfo API were extended to allow requesting multiple sizes, we could do a single request and retrieve all three thumbnail URLs at once. Will file a second bug to enhance ForeignAPIRepo to support this...