On this Memorial Day — as opposed to that other one, I guess — let us take a moment to figure out how people in 100 years will remember us. What will we leave behind? Can you imagine your headstone with your name, dates and a number of cumulative likes bestowed upon your Instagram pictures?

Modern photos are incorporeal, and you can lose them by accident in a trice, but the old photos weren’t a guarantee of immortality. Now and then I’ll be in an antique store and come across a box of studio portraits from the early 20th century. Everyone looks miserable, as if the photographer made them line their pants with sandpaper. You found happier faces in a 19th-century dentist’s office.

If someone does smile, they leap across the chasm of the years and come to life, and you can imagine them singing or telling a joke. But mostly they look as if life was an anvil to be dragged until you reached the grave.

If the photographer said, “Cheese,” it was probably preceded by “rancid, moldy.”

There’s a reason they look so dour: Getting your portrait taken was serious business, and something you did only a few times in your life. Levity was unbecoming such a moment. You were staring at posterity, and you wanted to hold its gaze as a sign of strength and character.

Posterity did not particularly care, though. Neither did the descendants, who cast off the pictures into the antique store for four bits apiece. When you turn the photo over, you hope there’s a clue — “Aunt Edna, Gustav and Ilse” — anything to keep these people from toppling over the lip of the chasm into anonymity.

But there’s rarely a name. Whoever had the photo knew who they were, after all.

The next generation inherits the albums, and puts them away on a shelf; the generation after that finds them when cleaning out the house and either joins a genealogy website, does some research and rescues the people in the pictures — or they get rid of them. Who are these people?

You’re more likely to be remembered if you bought a house, got sued or found a loose farm animal. A house title carries your bones forth as long as the dwelling stands, and the dates you bought and sold it are like covers of a novel in which all the ink has faded away. Court records are filed away for eternity. And, as for finding a farm animal, well, consider Mr. Owen.

Last week I was at the Dodge County Historical Society — a marvelous place, highly recommended; don’t miss the enormous hearse in the basement — and opened a book of Estray Notices. Said one such entry:

“Notice is hereby given that the subscriber has taken up a steer, one year old, a Stray, Color white and brown, or rather inclined to brindle, small horns. Dated at Ashland Nov. 13th, 1865. B.M. Owen.”

What does this mean? Simple: Mr. Owen, from Ashland Township, came across a loose steer and filed a notice with the local government that the stray was now his unless someone claimed it. The book is full of these accounts of vagrant beasts, each entry duly signed and dated.

Why does this matter? It doesn’t, except for this: I tell my family to back up all their phone pictures as often as possible, including cloud storage and hard drives, because if they lose their phone there will be more evidence of Mr. Owen’s steer from the year the Civil War ended than evidence of their last half-decade.

So ... where, you ask, am I going with this?

How about this: You will be remembered, but not forever. That’s OK, except it’s also sad, but it’s so common we can’t complain. Physical objects have more staying power than a digital image, which is why you should print out your photos and put them in books, so your descendants have something they can use.

Sure, you can put your pictures online, but there’s no guarantee they’ll be there tomorrow, let alone 10 years from now, and it’s a dead-cert guarantee they’ll be gone in 50. You can put them on a storage medium, but a decade from now, few computers will have the same plug.

Yes, it’s hopeless in the long run. But Memorial Day reminds us that it’s important to try. Carrying memories forward is a bucket brigade. Pitch in and help.

One more thing: NASA has announced that the next Mars Rover will carry thousands of names to the red planet. You sign up online, your name’s added to the list, and you will live forever in the circuitry of a robot on another planet.

It’s a nice idea. But here’s a better one: A private space company flies your photo albums to another planet and leaves them there, safe and never able to be discarded.

It’s one thing to have your memories backed up to the cloud, but backed up to the moon? Sign me up.