If you are the photographer then the copyright is automatically yours.
There are certain circumstances when photos have been taken on private ground with restrictions in force which would affect you selling these photos, or if you have been commissioned and paid for taking them.
If you are a little paranoid you can incorporate your copyright into the Exif or place a copyright statement on your photos.
The simple way in photoshop is to create a new brush. To do this create a new document approx 400 x 100 pixels. Type in your copyright. With this box open and text tool selected press Alt 0169 this will give you the copyright symbol follow this by typing in the year and your name if required.
Size of text or colour is unimportant at this stage,flatten the layers palette. Now go to Edit>>Define Brush Set. In the box that opens type in copyright and save.
To apply to a photo just select your copyright brush, select colour and size then click in an appropriate position