I recently was writing some code to apply a mask to an image input. The mask had no Exif metadata, but the image did, so I had to adjust for the orientation of the image by reading it from Exif.

This isn’t hard with libraries, and I knew the gist of the problem: images can have Exif, Exif is optional, phones and cameras use it for orientation, and you need to account for that when processing pixels directly. But I did not have a clear mental model of how Exif actually is represented in files.

I was curious. I had questions :

Where exactly is that orientation value stored? When should I rotate pixels instead of preserving a tag? What else might be hiding in the metadata? When is it typically stripped?

So this is a little random walk guide to Exif.

What is Exif?

Exif is short for Exchangeable Image File Format .…