How to store 30kb file using Decentralized Blockchain Data Storage on NXT (nxtcoin) by attach messages?
Seems that the new 1.5 nxt version is giving users the ability to attach up to 40kb worth of data in the blockchain. See here: 

NXT 1.5 decentralized storage on the blockchain

Also found the discussion of NXT Transient Data where data can be stored on the blockchain temporarily and then removed after a certain amount of time to reduce blockchain bloat. As discussed bye Jean-Luc: https://nxtforum.org/general-discussion/price-speculation/msg126548/#msg126548


  We could add a "transient data" attachment that can have larger size,
  but is only kept in the blockchain for a limited time, say 24 hours.
  The hash of the complete attachment will be included in the
  transaction bytes that are signed and will be kept permanently, so
  that transaction signature can always be verified, but the actual data
  will be deleted after this expiration period. Then the bloat to the
  blockchain and extra traffic will be limited to those attachments for
  the last 24 hours. This wouldn't be that useful for images for goods
  that sellers keep in stock permanently, but for short lived items, or
  even message with picture type of attachment, may work. Just an idea.


Decentralized file storage released on production blockchain: