Instructions
Focus on one element of the pictures at a time. For instance, comb the pictures for differences in colors. Then look for differences in sizes. Staying focused on one specific element helps you to spot changes more efficiently.
Turn the pictures sideways or upside down if possible, after you've looked for differences from the regular angle. Using an alternative angle can help your eye to catch things that you didn't see at first.
Enlarge the images if possible. Some online versions of this game allow you to enlarge the photographs, which makes spotting differences easier.
Begin with easier levels of the game. Learning to spot differences that are more obvious will help you to adjust to the process of looking for things that have changed from one photo to the other. Building success on easier puzzles helps you to stay motivated, as you work toward more difficult photographs.