Point-and-shoot and DSLR cameras have a knack for attracting dirt, and that grime can show up in pictures. Sand and moisture at the beach can render a good camera unusable. Here’s how to clean it up.

To check for dust on your sensor, use the longest focal length or zoom setting of your lens, focus to infinity, and use a narrow aperture of around f/16. Take a few shots of a blank area of sky and ...