The insects in the photos are booklice (family Liposcelididae). 

Booklice are common in many homes, where they are usually present in low numbers. However, their populations can build up under high humidity conditions. They generally feed on mold and are an indicator of high moisture but may sometimes feed on starchy material such as wallpaper and books. 

The best control measures are to reduce humidity and moisture by installing dehumidifiers in the rooms where commonly seen and fixing any sources of moisture (leaky pipe, clogged gutter, etc).