[qnr]

Nothing. The way arbitrary data is stored in the blockchain is encoding it in the financial transactional data.

For example, you could use a similar method to "store" data using Paypal: use the amount of cents in each transaction to encode a byte of data (e.g. $1.17 means 0x75 etc.) and make transfers to random people until enough bytes have been transferred. That's it, your copyrighted data or CP is now forever "stored" on Paypal servers.

I don't think this accusation will hold up in any reasonable court. Taking into account the cost of storing data (20 bytes in a single output of minimum 5400 satoshi + fees) your hypothetical instructions and code to retrieve the images would be of comparable size to any images you can reasonably store.

[maaku]

There is no minimum output size. Outputs can be zero-valued.

[qnr]

The standard client and by extension most miners will reject outputs smaller than a certain value ("dust")

You are correct that the protocol itself doesn't have a minimum output size, so if you mine a block yourself you can include dust reliably.