Avogadro Molecule Editor: How to render image from command line?
There is no way to currently do this using Avogadro, although Python bindings have been "in the works" for a while. The problem is, with volunteer developers, there's not always enough free time to tackle all features.

You can create pseudo-3D images using Open Babel. I developed this for the Pitt Quantum Repository to give SVG and PNG images in the search interface. It's not perfect, but I like the effect.

obabel beta-carotene.xyz -O beta-carotene-2d.svg -xS -xd -xb none




The -xS indicates this 3D "ball and stick" style, -xd prevents the molecule name from being included, and -xb none gives  transparent background to the SVG (useful for presentations).