Light-leak photographs are a great example of adding colors to an image and making it more fun as the image becomes vibrant and colorful. I would love to use this effect when on vacations, taking self-portraits or just when on the beach or so – adds a great touch to the images, not all images though.
This type of photography requires a specific camera or either you could always add the light-leak in from Adobe Photoshop (Lomo lights).
A little info regarding light-leaks from Wiki:
A light leak is a hole or gap in the body of a camera where light is able to “leak” into the normally light-tight chamber, exposing the film or sensor with extra light.
One frequent source of light leaks in 35 mm cameras is around the film door due to degrading foam.

Credits:
Robbie Swan, Erin Rena, B r e a t h e | F o r | L o v e, Erin Rena, Monica C. Salomon, Evan Jay Warren, i.am.you, elizabethmahoney, StevanFane, i’m a witch, Julia Yusupov, qwj, Violet Short (2), Abeera Khan, Tsaos