First of all, not only physical 3D objects might be hashed, but also virtual ones which have basically been generated. So, we have one more crucial option:
1. scan an object with a smartphone or special lab equipment and then get them hashed by means of processing
2. generate or grab somewhere a 3D model and then get it hashed as well. And, yes, it's also possible to print the object by 3D printer or just produce it in some other way.
These two options have the only one difference which is seed data extraction method. If you're using a 3D model just generated, you don't need to scan the object physically, although the outcome will be the same: .stl or .obj file. These kinds of standard files is leveraged by 3DPass.
Talking about mining, miners could use 3D models generator in hope of finding a specific-shaped object the hash id of which would include zeros at the beginning. It's required to get rewarded from the network. Mining is expected to last about 60 years. And it serves mainly as a distribution mechanism. At the very beginning it will be possible to use smartphones to create the right hash, but it's the way less efficient then objects generation.
We're considering an alternative paid option to create a new block with. Especially, it would make sense after the mining finished. E.x. someone has published their object and its hash id for the reason of utilization (to make deals with, mint currency, etc). What they have to do is to pay commission in 3DP for the validation service providing by nodes. If the validation is successful the new block is going to be created. It's expected people will use the network after 60 years being on the market. How much the commission fee will cost is up to the nodes to decide.
So, we hope the network will never come across with the lack of objects to create a new block out of.