Is there any data available on the general use of audio clips (30 second) and
album artwork (thumbnails) on websites? I'm interested in the global picture but
particularly Europe and the UK. Specifically...

1. The usage rights are generally considered to be a grey and complex
area, what assets and what uses need to be licensed and if so from
whom?
2. Who are the major suppliers/users of clips and artwork and what do
they charge/pay?
3. How big is this market?
4. How does it work? ie do people usually host these assets themselves
or use the third party?