There are already a few great answers.
But to elaborate on the Layer method...

Once you've put the image on its own layer, double click the Layer icon, or use the Layer Options side menu, or switch it to Template in that same menu, to turn the layer immediately into a Template layer. This will automatically lock the layer, dimits content, set it to non-printing, and rendering it normal in Outline mode.

This makes it super-easy to do precise drawing !

Oorspronkelijk geplaatst op Quora: How do I keep an image locked in place in Adobe Illustrator?"