In order to display icons in software-centers, distributors should offer a repository of cached icons for applications defined in their AppStream XML files. The icons should be PNG files or vectorgraphics (PNG is preferred) and match the name referenced in the applications .desktop file. Their size should be 64x64px, it is okay to just provide one size.

All icons of type cached must be placed in /usr/share/app-info/icons/%{origin}/%{size}/ or /var/cache/app-info/icons/%{origin}/%{size}/, where origin is the AppStream data origin defined in the AppStream data file (see Section 3.1.3, “General XML structure”), and size is 64x64 or 128x128 depending on the size of the icon. And icon might be present with different sizes in both directories.

For example the cache icon krita.png of a component in a data file with the origin jessie should be stored in /usr/share/app-info/icons/jessie/64x64/krita.png (or in the /var/cache location).