How to safely offload camera cards on a Mac
Copy the whole card to at least two drives, verify every copy against the card with checksums, and only format the card in the camera once both copies check out. Dragging files in Finder skips the verification step, so use an offload tool that checks each copy, or compare checksums yourself before wiping anything.
Why a plain Finder drag isn't enough
Once you format a card, the only copies of those photos and clips are the ones on your drives. Finder copies files without ever reading them back, so a card reader that stalls for a moment or a drive with a weak sector can leave a damaged file that looks perfectly normal in the folder. Usually you only find out in the edit, after the card has been reused.
A safe offload adds two things: a second copy, and proof that both copies match the card.
Step-by-step: a safe offload workflow
- Lock the card. If it's an SD card, slide the write-protect switch so nothing on the Mac can modify it while you copy.
- Use a good reader, plugged in directly. Avoid unpowered hubs and long adapter chains. Most card-reading errors come from the connection, not the card.
- Copy the whole card, not just the clips. Many video cameras store metadata in folders next to the media files. Keep the folder structure intact, ideally in a folder named with the date and card number.
- Copy to two drives. Following the 3-2-1 rule (three copies, two kinds of media, one off-site), the card plus two drives gets you most of the way there on the shoot day.
- Verify both copies. Read each copy back and compare it with the card using checksums. See how to verify a file copy on Mac for the Terminal commands.
- Keep the record. Save the checksum list or report next to the footage so you can check the backup again later.
- Eject, then format in camera. Format the card in the camera that will use it next, rather than deleting files on the Mac.
Doing it with VerifiedCopy
VerifiedCopy handles steps 3 to 7 in one pass:
- Drag the card in and pick up to three destination drives. Each file is copied to all of them.
- Every copy is read back and checked with SHA-256, chunk by chunk: each chunk is written, flushed to the drive, read back, and compared with the card. If a chunk doesn't match, just that chunk is rewritten from the card and checked again, so a 50 GB card never has to be offloaded from the start. A full-file SHA-256 check follows by default.
- Optional auto-dated destination folders keep each offload separate, and pre-flight conflict scanning catches filename clashes before anything is written.
- Each job can save a CSV or JSON report to every destination. The JSON report lists the SHA-256 hash of every chunk. To re-check the backup later, run Verify & Repair against the card or another known-good copy.
- Set a post-copy action to eject the drives when the job finishes.
It also remembers your backup drives and recognizes them when plugged in, and you can start an offload from Finder's Services menu or the Shortcuts action.
Other offload tools
Dedicated DIT applications such as ShotPut Pro and OffShoot (formerly Hedge) are widely used on professional sets and add features like MHL reports for post-production handoff. VerifiedCopy is a lighter, general-purpose Mac utility: one-time $4.99, no account, fully offline, and useful for any files, not just camera cards.
| Tool | Verifies each copy | Multiple destinations | MHL reports | Runs on |
|---|---|---|---|---|
| Finder drag | No | One per drag | No | macOS |
| ShotPut Pro | Yes, checksums | Yes | Yes | macOS, Windows |
| OffShoot | Yes, checksums | Yes | Yes | macOS, Windows |
| VerifiedCopy | Yes, SHA-256 per chunk, then full file | Up to 3 | No (CSV or JSON report) | macOS 14.0 and later |
Pick whichever fits your workflow. What matters is that something verifies the copy before the card is formatted.
Offload checklist
| Check | Why |
|---|---|
| Card locked | Nothing can modify the source mid-copy |
| Whole card copied | Keeps metadata and folder structure the camera's software expects |
| Two destination drives | One drive failing doesn't lose the shoot |
| Both copies verified | Proves each copy matches the card byte for byte |
| Record saved | Lets you re-check the backup months later |
| Formatted in camera | Only after everything above passes |
Frequently asked questions
Should I delete photos from the card on my Mac?
It's better to format the card in the camera after you've verified your copies. Formatting in camera sets the card up exactly as that camera expects and avoids leftover files or a fragmented card.
How many copies of a shoot should I make?
At least two copies on separate drives before you format the card, and ideally a third kept off-site later. That's the 3-2-1 backup rule: three copies, on two kinds of media, with one off-site.
Do I need to verify copies to a fast SSD?
Yes. Verification protects against problems anywhere along the way, including the card, the reader, the cable, and the destination drive. A fast SSD makes verification quicker, but it doesn't remove the need for it.
Does Lightroom or Photos verify imports?
Photo app imports generally copy files without reading them back to compare checksums. If your app doesn't explicitly say it verifies imports, offload and verify the card first, then import from the verified copy.
How long does a verified offload take?
A verified copy reads the data twice, once to copy and once to check, so expect it to take longer than a plain copy. How much longer depends mostly on the speed of your card reader and the slowest destination drive.