The file you will need is the one from Tuesday

History is not a safety net

The History panel holds a list of recent states you can step back through. In Photoshop the default is 50; each state on a large document can cost tens of megabytes of scratch space, which is why the number is not higher.

Three things people assume about history that are wrong:

It is not saved with the file. Close the document and the history is gone. Open it tomorrow and there is one state.

It is linear by default. Step back five states, make a new edit, and the five you stepped over are destroyed. Photoshop offers Allow Non-Linear History in the History Options, which keeps them, at a cost in memory. It is off by default.

It fills up. Paint fifty brushstrokes and the state you actually wanted has been pushed off the end.

Snapshots partly fix this: click the camera icon and the current state is pinned, immune to the rolling window, until you close the document. Take one before any large irreversible operation. It still dies when the file closes.

GIMP’s undo history behaves similarly and is bounded by a memory setting in Preferences. Krita’s is also memory-bounded and, unusually, it can be configured to survive a crash through its autosave and recovery system.

Versions: the part that actually saves you

The reliable record is files on disk with different names.

A naming convention that works and sorts correctly:

honey-500ml_front_v01.psd
honey-500ml_front_v02.psd
honey-500ml_front_v03-client-notes.psd
honey-500ml_front_v03_APPROVED.psd

Zero-padded numbers so v10 does not sort before v2. A short reason attached to versions that are not routine. The word APPROVED, or FINAL, used once and never followed by FINAL2: if a revision comes after approval, it becomes v04.

Save a new version at each of these moments: before a destructive operation you cannot undo later, before sending anything to a client, and after a client approves. Three saves a job, and every one of them has a specific future use.

The habit that costs the most when missed: save a version before flattening. Flatten is the one command that turns a working file into a picture, and it is a single keystroke away from Save.

Backups: three copies, two media, one elsewhere

The standard rule, and it is standard because it survives the four realistic failures.

• Three copies of anything you cannot recreate.
• Two different kinds of storage: the laptop and an external drive, not two folders on the same disk.
• One off site: a different building, or a cloud account.

The four failures it covers: the drive dies, the laptop is stolen, the building floods, and you delete the wrong folder. Only the third is rare.

Free tools do this well. rsync -a --delete source/ destination/ mirrors a folder to an external drive in one line and runs in seconds on subsequent passes because it copies only what changed. On Windows, robocopy /MIR is the equivalent. Both are built in.

The trap in cloud sync

A synced folder (Drive, Dropbox, OneDrive, iCloud) is not a backup. It is a replica. Delete a file, and the deletion syncs. Corrupt a file, and the corruption syncs. Ransomware encrypts a file, and the encryption syncs.

What sync services do provide is version history, usually 30 days, which recovers the Tuesday file. Learn where that is in the service you use before you need it, because finding it during a crisis is a bad time to learn. And know its limit: 30 days is not an archive, and files removed from the sync folder eventually leave the version history too.

A real backup is a copy the live system cannot reach and overwrite.

When a file will not open

Large layered files do occasionally corrupt: an interrupted save, a full disk, a flaky USB drive during a write.

• Do not save over it. Copy the broken file somewhere else and work on the copy.
• Try opening it in a different application. Photopea and GIMP both recover partially damaged PSDs that Photoshop refuses, because they are more tolerant of malformed sections.
• Photoshop writes a flattened composite inside every PSD for compatibility with other software. If Maximise Compatibility was on when it was saved, another application can often pull that composite out even when the layer data is unreadable. That setting costs file size and buys you this. Leave it on.
• Krita and GIMP both autosave recovery files; check the recovery prompt on next launch rather than dismissing it.

What none of this solves

Versions and backups protect the file. They do not protect the decision. Six versions in, nobody can remember why v03 looked better than v05, and comparing them means opening both.

The cheap fix is a plain text file beside the images (notes.txt), with two lines per version saying what changed and what the client said. It takes fifteen seconds and it is the only part of this lesson that survives you leaving the job.