All, I am just re-learning Blender after a 4 year absence.
I am trying to add some 3D objects to a photograph so that part of objects appear to be behind elements within the 2D image.
I thought my problem had been solved with this video tutorial (below), but upon trying it found that the sticky texture feature has now been removed.
Is there another way of achieving the result I want?
many thanks in advance
Interesting! I didn’t know this technique but I’m (almost) sure that this is not the optimal way to do it.
Ideally, one should use layer masks, this is what they are for and it’s easier to setup and use.
Is there a tutorial on how I would use layer masks to achieve this effect?
Are there any tutorials that show how to use layer masks to achieve the result I am looking for?
Search UV Projection and Camera Projection, UV Projection was introduced into blender to get over some of the issues with the sticky coords idea, then stickys were dropped in favor of UV projection.
I have posted some experiments here, and find that you need the right amount ofsubdivision and editing (add cuts to mesh) along frame edges to make it work without strange distortions.
The concept is elusively simple so I reckon that you don’t really need a tutorial for that.
If there’s interest, though, I guess I can make a short one.
Here’s a very quick illustration with a cc licensed sink image I got off wikimedia:
And here’s the noodle:
As you can see it’s nothing really special and the setup is very simple.
All you need is a single render layer for such a simple masking effect.
Susan goes on one layer (top leftmost) and the plane masking the sink on the layer below it.
Note that on the masking layers panel you need to activate the layer which will be used to mask (i.e. hide) the layer where Susan resides. Obviously, due to the setup, it will not mask all of Susan, just a small part of her and this can be determined through proper object placement in the 3d viewport.
Hope this makes sense! 
