Humidity isn't good for any of your home furnishings, but it's especially bad for your framed paintings and photographs. When moisture seeps behind the glass, it creates an environment for mold to grow in the paper or fabric of your artwork, which can cause permanent damage if you don't do something about it. It's important to dry out any affected pictures, but by itself, that may not kill the mold, and treating the pictures with any type of liquid disinfectant may damage them. One solution is to use an aerosol disinfecting spray to kill active mold.
Put on a respirator to protect yourself from airborne mold spores. Take the backing off the picture and remove the picture from the frame. Lay it face-up on a clean, flat surface.
Use a hair dryer set at a low temperature setting to dry the picture if any part of it is wet.
Spray active mold, which appears black or dark brown, with an aerosol disinfecting spray. Dust the spray lightly over affected areas on the front and back of the painting, being careful not to saturate the canvas or paper. Let the spray dry -- do not wipe it off. The mold should turn gray and powdery; if some black or brown mold remains, repeat the treatment.
Take the painting outside and brush off the dormant mold spores with a clean, dry paintbrush.
Remove the glass from the frame and spray it, as well as the frame, with the disinfectant spray. Take both outside to brush off the dormant spores, then wipe both down with a solution of 1 cup of bleach per gallon of water. Let both dry.
Clean both sides of the glass with glass cleaner; wipe it dry and put the glass and picture back in the frame.