Figured it out. Busy points to `https://steemitimages.com/p/2r8F9rTBenJR3iqPxDrevHK3vDeQGnHc8Wj8AHaVaNFK2GQkaBiypyoztqDRGqyKYSmm6CgiPrm4nPQBJ4JnYC7q8HGTHN1ShohiAihkEuuMCDBdfEFATphzNxkqi1baY?format=match&mode=fit`

If I remove the `?format=match&mode=fit`, the image is shown. Otherwise, I only get the `upstream_error`.

Steemit points instead to `https://steemitimages.com/p/7DceLftyMsyfyqUUPmYDrL2rVNFTCb39NCVCK2jKJ4ZDYr6GMeve2sZTpoDPC5zCUNqdvyULnhtCVwW2kf6Jc?format=match&mode=fit&width=60&height=70`

Hmm. That one works too. The latter also works with `?format=match&mode=fit` only. Strange.