Digital photography has not brought us the world of special effects, but it has made creating them such a lot easier. In conventional photography effects could only be applied by spending painstaking hours in your darkroom, dodging or burning-in parts of an image, multi-exposing photographic paper, using toxic chemicals for toning or making complicated cardboard masks to create something special.
Nowadays image manipulation programs make effects like these a doddle, since digital images only consist of bytes on your computer that can be played with to your heart's content.
Dodging or burning-in of image parts can be done by selecting certain parts of your image and applying filters to those areas only, leaving the rest unaffected. Make a mistake and you simply start again whereas programs such as Photoshop even have a History function to let you trace back your steps and correct as necessary.
Changing backgrounds, using special effects filters, pasting parts of one image into another, it can all be done. Selenium, sepia or blue toning, infrared effects or motion blur filters, the possibilities are endless. Your own imagination or creativity is the only limit to what can be achieved. A number of outside companies even provide “plug-ins” for programs such as Photoshop, making the number of creative effects even larger.