What is the logic to having an axis labeled Z and also having Z refer to distance from the camera? It seems like an easy way to confuse people. Is this due to the conjunction of two different lexicons, one from geometry where they have a Z axis and one from photography?
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I'd say it's more about different reference frames. There's the world coordinate frame. Then there's another coordinate system for each object (mesh, camera, whatever). And in armatures each bone has its own coordinate system (and mapping from one bone's coordinate system back to world space goes through every bone in the parenting chain). – Mutant Bob Mar 31 '15 at 20:48
2 Answers
Quoting from iKlsR's answer:
Blender uses the right hand coordinate system with the Z axis pointing upwards. This is common with the coordinate systems used by most common 3D CAD packages.
However, it's also a standard to use Y up for images (with Z as depth).
To help with getting used to it, you could try a couple things:
Imagine you are looking at the image editor top down instead of from the side.
Think in terms of the camera's local coordinates (the local Z is always out the front)
In blender Z is up in world space. In the camera Z is also the distance from the camera. There are many cases where the Z axis are not the same and could potentially confuse you. In this image the object is upside down. In world space Z would be pointing up. In local space it is pointing down.

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