Assumption: (non default/missing) box art never changes.
Therefore: collect only once then periodically check for broken/default box art and then manually trigger a force update for box art you know has changed. As in never poll the WHOLE inventory twice…
Suggestion: find a source that has a commercial use policy (yay licensing fees this stuff ain’t free you know).
Suggestion: curate your own box art (this has it’s own licensing issues)