These only work in the `selectThumbnail` component. If it's small enough, it'll get past the transaction limit-check, but ultimately it doesn't appear correctly in the claim list.
It'll probably appear correctly if we tweak the ClaimPreview code, but since this also fails the Google Video metadata test, I think we should disallow this.
## Issue
5923
Thumbnail errors were just being used in `selectThumbnail`. The form doesn't know about it and was using allowing invalid thumbnails like 'helloworld' to pass through.
