Although there are many kinds of photos, there are a few simple ways of protecting them.
First, and most important, is to prevent any UV light from reaching the photo. It is vital for any photo that is on display to have genuine Museum glass, which is designed to filter out all UV light.
Second, photos are all made from a great variety of chemicals. To be safe, you should assume that your photos will suffer if exposed to anything other than 100% cotton rag Museum Mat board that is totally free from the "buffering agent" called "calcium carbonate". Calcium carbonate can react with some photos and yours may be sensitive to calcium carbonate. You don't want to find out the hard way, when it is too late!
If you have valuable art, never leave it to the "TLC" of a frame shop! It could be damaged, or, even stolen! (I once knew a framer who admitted to accidentally erasing part of an Ansel Adams signature. Instead of telling the customer, they faked the missing letters.) So, be there when the art is measured, place your order, and make an excuse such as: the insurance company requires that the art be with you, therefore you must keep it at home. Once the Museum Mat and glass are ready to go into the frame, then, return and wait while it is assembled - in front of you - so you can watch.
If a frame shop does NOT stock 100% cotton rag Museum Mat board - walk out! - They are not the best. (Note - the Rising Co. makes - or used to make - a mat board called "Photo White ", that has no calcium carbonate, only 100% cotton. They may also have (or had) an "off white" - also, without the calcium carbonate.) I am not 100% sure, but I think that the Strathmore Co. may also have offered a calcium carbonate free mat board. It may have been a "photo gray". I don't know about their current products.
If any frame shop offers you a so-called "acid free" mat board, claiming that it is "just as good" as 100% cotton Museum Mat board - walk out! That crap is chemically treated wood pulp, and it will re-acidify! And, it is almost certain to have calcium carbonate.
The back is as important as the front! Demand the exact same Museum board on the back of the photo as on the front. And, check it to be sure!
The photos need to be held in place. To do this you need acid free tape on the back of the photo. The tape (hinges) that touch the back of the photo must be acid free! Acid free linen tape may be the best choice. The paper/paste option is difficult because it gets the photo wet and that could present problems of warping. Also, some photos may be sensitive to water, and worst of all, water based tape could create mold.
Now, about the "dust cover", a.k.a, the "cover-up". Actually, very little dust gets behind a picture. Most dust is on the frame (including cobwebs) and on the glass. (Note - Beware, the pretentious places call glass by the snotty term "glazing".)
A so-called "dust cover" covers up the back - so you can't see that they didn't use museum board - maybe they used foam core, or even cardboard. You don't need a "dust cover" unless you live in a sawmill.
Moreover, the "dust cover"-up gets in the way of the wires, which are needed to hang the picture, and it is often punctured by the hook, or hooks, that support the picture. Finally, and maybe most important - if there is a "dust cover" - then all changes in airflow (which are inevitable) are forced by temperature changes to go around the edges of the glass and impact the most delicate surface of all; the photo. So, it is best if the pictures including the mat boards, (front "window" mat, and the back board) "breaths" from the back. Or, you could simply cut open the paper backing when you get home. In this way you can check to be sure that the backing board is really 100% Cotton Museum Mat Board.
Never, ever, hang a valuable picture:
Only hang valuable pictures on inside walls, away from the dangerous places mentioned above.
Never store any art in cellars or attics.
And, never allow anyone - other than yourself - (or, a conservator) to clean the glass, or, even dust the frame. (See: section on Cleaning) Because they could easily ruin, either the picture, the glass, or the frame.
This covers the basics on getting photos ready to hang up. Please see Storing Photos, (including negatives and slides) and, Archival Digital Storage.
P.S. This usually means Post Script, and it does here, however, it also - in this case - stands for "Pathetically Stupid".
I'm talking about the moronic process of "Dry Mounting" photos, (or any art) to a mat board. DO NOT DO IT!
I once had the extreme, and sad, experience of seeing a ruined photo by Ansel Adams. He had "Dry Mounted" it to a mat board. The mat board warped so badly that a vertical 8x10 photo was transformed into a series of "waves". Viewed from the side it would look like this:
There was NO WAY to fix it. Any attempt to flatten it would have deeply cracked the surface of the photo - thereby destroying (or completing the destruction) of a genuine Ansel Adams photo. I knew that the only hope for it was a professional Museum Conservator - with the patience of Job. I refused to mess with it, even though the customer asked me to try to "fix" it. Tragic! And, unnecessary.
So, where does the "Pathetically Stupid" come in? You should have guessed by now. It is Pathetically Stupid to "Dry Mount" any art. It is the tragic flaw in the minds of West Coast photographers - and they are the ones with the "idée fixe" that their photographs are only "real art" if they are "dry mounted" to a mat board - presumably, so that they can sign the board in pencil. (Reference - the story of the framer - cleaning a dirty board - and carelessly erasing part of Ansel Adam's signature!)
I realize that this critique may well offend some West Coast photographers. Good! In the name of God - and common sense - stop it! Stop "Dry Mounting" your work! Because, from time to time you actually manage to create a good picture. Not as good as the great Alfred Stieglitz - to whom Ansel went for recognition and approval - but you do, sometimes, make good art. So, STOP RUINING it with "Dry Mounting", Damn It!
Don't you realize that Stieglitz, the father of Modern Photography as an art form - has already "kicked" the door in, when, circa 1920, the Boston museum of Fine Arts, had an exhibition of his photographs? Your insistence, on the idiotic process of "Dry Mounting" your work betrays a basic insecurity, and self-doubt. Worse, the process is - as far as I know - totally irreversible, and damaging to the photographs! Do you imagine that the heat that is needed to "Dry Mount" anything does the longevity of your photos any good? Stop it! Would you "Dry Mount" a Rembrandt etching? Of course not! Realize now, what you SHOULD have known, nearly 100 years ago. The deed is done! Thanks to Alfred Stieglitz, with the help of the Boston Museum of Fine Arts, photography IS - in fact - (if it is of the highest quality) already, and since 1920, an art form! Got That?
You don't Need to sign the mat boards! Sign the photo! Use a very fine pointed pen with archival ink! (The Sakura Color Products Corporation - in Japan - makes great pens called, "MICRON", with many sizes for the writing tip, and acid free, archival ink! So, Think! Protect your work. Sign the photo.
So, now that I have vented my concerns and frustrations - over the idiotic practices - of West Coast photographers, resulting from their insecurities: (without apology, because I'm telling them the truth!) I want to go back to the genuine art lovers, much more gently! Please NEVER make the mistake of "Dry Mounting" any art work!
The only value in the "Dry Mounting" process is found, when - for example - you have a work of art that requires a mat board - and the mat would be more attractive if a fabric - such as a lovely silk cloth - were to cover the mat board that forms the "window" around the art work.
Now, when this is done you will still have a bevel around the Art Work that is the color of the mat board itself, provided that you have a genuine Museum mat. (Note - See section on Museum mats.) If you desire to have the bevel covered by the fabric, then you still need to have another Museum Board under the fabric wrapped board. (Note - See section on Museum mats.)