Guides

How to tell if an SD card is fake

You can't tell from the label, the packaging or what your Mac says the card's size is. A fake card is reprogrammed to report a big capacity it doesn't have. The only reliable test is to write data across the card's whole claimed size and read it back. On a Mac, that takes about a minute with a free tool.

How fake cards work

A counterfeit card has a small amount of real memory, say 32 or 64 GB, with its controller set to report 512 GB or 1 TB. Everything works normally until you've filled the real memory. After that, most fakes quietly throw away anything new: the files still show up on the card, but open gray, garbled or empty. Some instead write over your earlier photos. Either way there's usually no error, and people find out when they get home and half the trip won't open.

Warning signs

• A big card at a price far below what the same capacity costs from the brand's own store.
• Sold by an unknown seller, especially through a marketplace, with spelling mistakes or odd fonts on the packaging.
• Photos that open but turn gray or scrambled partway down, or files and folders that disappear after the card has been used a while.
• A speed test that shows a card much slower than its label.

None of these prove anything on their own. Genuine cards are sometimes on sale, and fakes can look perfect.

Why "Get Info" can't tell you

Finder shows the capacity the card reports, and a fake reports the fake number. A genuine card also shows a little less than its label, for example just under 64 GB for a 64 GB card, because some space holds the file system. That's normal. The question isn't the number, it's whether data written near the end of the card comes back.

How to test a card on a Mac

Shutterkit Check (free)

Shutterkit Check runs a Quick Check in about a minute. It writes small test blocks across the card's whole claimed range, reads them back, and then puts your original data back, so it doesn't erase the card. If the card is fake, it tells you its real usable size and gives you a report to send the seller. (We make it.)

F3 (free, open source)

F3, "Fight Flash Fraud", is a long-standing open-source tester. On a Mac, install it with Homebrew (brew install f3), then run f3write to fill the card's free space with test files and f3read to check them. It's thorough, but filling a big card can take hours, and it runs in Terminal.

On Windows

H2testw is the classic free tester. It works the same way as F3.

If your card is fake

1. Copy anything you need off it now. Files written past the real capacity may already be damaged.
2. Stop using it for anything important.
3. Ask for a refund from the seller or the marketplace and report it as counterfeit. Keep the test report as evidence.
4. If photos are already missing, recovery software may find some of them; see how to recover photos from a card.

Make it a habit

Test every new card before you trust it with a shoot. It takes a minute, and it's the only way to know.

Updated October 11, 2026.