First, I bought archival boxes to lay photos flat, organized by family, rather than having them filed vertically in a folder. Next, I put every single photo into a clear, acid-free, protective sleeve or resealable envelope for long-term storage and protection. (Vendors who offer boxes and sleeves are mentioned on a number of sites, including on Cyndi's List.)
The recommendation to "put a sleeve on it" comes from multiple expert sources, such as:
The caption on this photo explains not only who the boy on the pony is, but why a pony is standing on the sidewalk in front of a Bronx apartment building, circa 1919. Future generations may not know that entrepreneurs brought ponies to street corners, offering "photo opps" for kids of city dwellers at a low price.
I really want my heirs to know! And for now, a scribbled caption is better than no caption at all, right?
PS: Don't forget to inventory the photos. See "sample templates" on the tab above right.
Want more detail on "how to" sort photos, preserve them, and decide what to keep/what to give away? Please check out my new book, Planning a Future for Your Family's Past.