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.
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).
@ sign. If the scaling factor is 1, it must be omitted from the directory name. For example, if the icon scaling factor is 2 for icons of size 64x64 from origin jessie, the icon must be placed in /usr/share/app-info/icons/jessie/64x64@2/.
Legacy Support
64x64 pixels.