As some of the answers have indicated, a key issue in copyright is proving creation date and ownership of the original. This problem is especially acute with digital images.
There is a simple cost free solution.
1. Create a Google account like email@example.com
2. For every batch of images that you wish to protect, send an email to this address containing
2.1 a small jpeg version of the original containing the exif data.
2.2 the MD5 checksum of the RAW original.
Since Google Mail is a trustworthy repository
1. the date of the email is proof of the registration date
2. the record of the MD5 checksum is proof that you own the original, since the MD5 will only match the RAW original in your possession and only you know the password to the email account. (including the RAW original might quickly exhaust your storage allotment in Google Mail)
There are commercial entities that supply digital repositories intended to solve this problem. They all suffer from one acute problem - you have no assurance that they will still be in existence in say, 10 years time. If their business model fails your copyright proof evaporates. Currently, outside of national archive bodies, Google is probably our best bet.