Shweta, I found this information online that explains it well. It is found at, http://www.aaronbrothers.com/canvases/faqs/
"I would like to hang a picture in my bathroom, but worry about moisture. Can I seal the frame to prevent moisture from seeping in?
"Completely sealing a framed item is a difficult and problematic issue. When required for the preservation of a valuable item that cannot be displayed in an area with a stable climate, it generally involves in using a heat-activated adhesive to adhere a polyester and aluminum laminated sheet to the front edges of the glass, wrapping it around the side, and covering the back. Sometimes, a desiccant or conditioning material will be included within this package to help maintain a stable and low moisture level. Since humidity is relative to temperature, however, even sealing the item completely does not guarantee that fluctuations in temperature will not cause problems. It is also a fairly expensive solution.
"In practical usage for decorative items, your best bet is probably to simply slow the rate of change in moisture content within the frame to minimize condensation, rather than try to prevent it altogether. This can be accomplished through the use of ample filler boards in the back of the frame, which help to buffer this sort of change, the standard dust cover, and the use of bumpons to ensure air circulation behind the frame. If the back of the frame is in direct contact with the wall, it can wick condensed moisture from the wall into the framing package. A little air space behind the frame helps to prevent this.
“If you notice condensation or buckling of the matting even with these measures, you might also consider a non-traditional framing approach, such as the Colorplak process we offer. This involves mounting and laminating a print to a rigid backing with edges that are beveled and finished in your choice of colors. Although it does not allow the use of matting, it is a “sealed” solution that is safe for hanging in very humid environments, such as a bathroom.”
The only thing I would add, is that the picture needs to be “refreshed” every 3-5 years. This means that it needs to be taken completely apart, cleaned, and checked for moisture damage. Sometimes ghost images can seen on the inside of the glass. Refreshing needs to be done on all art, not just the ones in the bathroom (it just does not need to be quite so often).
Lori