You talking about an oil painting? They are notably resistant to fading. And I believe fresco also is resistant to fading.
The ink used in prints will fade....but it's very usual to put a print behind glass....and if you use non glare, UV resistant...you won't notice the glare. The non-glare glass does change the colors slightly though.
Of course if you spend thousands of dollars on a very large oil to hang opposite a wall of windows, I would consider covering with non glare UV resistant glass. I have noticed major museums often have pictures on loan that are covered with glass....I suspect that's a condition of the loan.
Linda C

Thanks so much for your reply. I have just started searching, and don't have anything in mind yet. Previously, we had a very large print over the fireplace, and it faded horribly. Good to know about oil paintings being resistant to fading. There are numerous antique and 2nd hand stores around my community, so I'm hoping I can find something locally without breaking the bank.

There are also window films you can put up on the windows to cut the damage the sun does.
Just remember if it's fading out a poster or painting it's also doing damage to any fabrics you have in that room too.

I have large oil portraits of each of my children, and the artist applied some sort of wax to each for protection. I don't know if it is uv protection or some other type of protection, but I have had my son's portrait for 7 years and my daughter's for 3 and have had no problems with fading at all.