One excellent use case for Blockchains is digital stamping. Imagine it like a digital notary service, but contrary to a traditional notary service you don't need a trustworthy third party. The blockchain itself provides all the characteristics of a trusted third party: it facilitates secure online transactions, it is a decentralized and distributed network, and registered transactions cannot be altered retroactively. This allows the participants to verify and audit transactions in an inexpensive manner.
Stamping a file on the blockchain proves that the document existed at that particular point of time. If the user has signed the document before stamping, then he may undeniably claim that the document was in his possession at the time of the stamping.
Another advantage is that you can prove the files origin, date, authenticity and integrity, without exposing its contents.
For example Bob composes a new tune on his computer. After he has saved the document a small app automatically creates a digitally signed timestamp on the Bitcoin Blockchain. His acquaintance Chuck visits a couple of days later and listens to the new tune. Unfortunately Chuck is also a musician, but not very talented and currently not creative at all. So he decides to steal the song from Bob. A couple of weeks later Chuck releases "his" new song.
If the blockchain stamped tune is indeed original authentic non-stolen & non-copied work signed by the user and if no other previous public statement on the stamped content may be found anywhere then Bob has a very strong argument to also claim authorship.
The timestamp on the Blockchain can be used to notarize any media file, e.g. plain text TXT, Portable Document Format (PDF), Microsoft Word (DOC, DOCX), Image (TIFF, JPEG etc), Spreadsheets (XLS, XLSX), Drawings (CAD) with any kind of content like: Contracts, Photos, Literature, Drawings, Books, Poetry etc. It can be used for digital attribution, proof of existence, prior knowledge, integrity, authenticity.
The stamping is fully decentralized (as is the blockchain itself), thus no third party or centralized internet service is required for the user to prove the certification of the document in the future. The user will be able to prove the document stamping by referring to the pertinent posting of the document’s imprint (hash) on the publicly available blockchain.