Picasaweb / Plus Instant Upload images are stored seperately from Drive. This is unfortunate because it means you can't use Drive APIs and tools with synced images. In particular, Drive exposes public files via well known URLs while the situation with Picasaweb is much less rosy.
- Google product forum complainies.
- Stackoverflow post leading me to some answers.
- This page doesn't tell how to get the URL for a specific image but it links to one that does.
XML Pretty Print is useful, since
?alt=json doesn't seem to work on all endpoints.