Metadata is data embedded within a digital work to provide information about it, most importantly to declare the works copyright status, declare who the copyright owner is and their contact details. All digital works, such as photos for example, should have embedded metadata and it is the creator who must take responsibility for doing so with every digital work they create.
Metadata makes it clear who owns the work and who to contact for permission to use it. Never omit to embed metadata in your digital works. Failing to do so can render your work an 'orphan' in that no one can easily determine who owns it. Unscrupulous organisations may use your 'orphaned' work in the knowledge that you are unlikely to find out. Even if you do discover that it has been used without your permisssion, you may find your legal remedy against the infringer of your copyright somewhat compromised by your own neglect to properly assert your rights. Don't let that happen to you.
Some contests requested that entrants remove metadata from their works before submitting them to the contest. NEVER ever remove your metadata from your works in order to submit it to a contest. Likewise no contest organiser should seek to remove, add to, or alter any rights metadata present in your work.
Note also that some websites, particularly social media website such as Facebook and Twitter, delete all metdata, including name of the owner of the work (i.e. the copyright owner). Some competition organisers use Facebook to host their competition. Don't submit photos or any other creative content such as music to these sites.
If you would like to know more about copyright and related rights please read our Guide to Rights and Licensing.