Comment 4 for bug 1626494

I'll pick gnome-calculator as an example since it shows stretched in both Xenial and Yakkety.

The issue seems to be the appstream generator is making stretched thumbnails and gnome-software / appstream-glib is choosing these over the original images. For gnome-calculator (which shows the problem in both Xenial and Yakkety) the dep11 data [1] gives:

From
    source-image:
      height: 285
      url: g/gn/gnome-calculator.desktop/849e24a42d3d86f364e068fc3be7f680/screenshots/source/scr-1.png
      width: 312
    thumbnails:
      - height: 702
        url: g/gn/gnome-calculator.desktop/849e24a42d3d86f364e068fc3be7f680/screenshots/1248x702/scr-1.png
        width: 1248
      - height: 423
        url: g/gn/gnome-calculator.desktop/849e24a42d3d86f364e068fc3be7f680/screenshots/752x423/scr-1.png
        width: 752
      - height: 351
        url: g/gn/gnome-calculator.desktop/849e24a42d3d86f364e068fc3be7f680/screenshots/624x351/scr-1.png
        width: 624
      - height: 63
        url: g/gn/gnome-calculator.desktop/849e24a42d3d86f364e068fc3be7f680/screenshots/112x63/scr-1.png
        width: 112

The large thumbnails are distorted and should not be used/generated.

[1] /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_yakkety_main_dep11_Components-amd64.yml.gz