Flickr licence?

which licence should i put on my pictures if i put them in contests and is there a way to change all the licences at once?

You should probably look into one of the Creative Commons licenses, which allows you to retain rights to the work whilst allowing others to use it.

You can change you Account Preferences to the license you want. This will set the license for all the photos you upload after you make the change. You can also change the license for batches of photos.

Creative Commons also has a wizard that you can go through to help you determine the license right for you.

You can find all of these links in my sources section.