Allow for the view/export of any inventory created, and also offer the ability to merge them manually. I feel like you need to go after the AFOL/TFOL market here, before trying to make a walled garden of mocs. AFOLs/TFOLs may have very large collections which don't scan in a single pic. If your market is parents who have some random bricks for their young child, I feel that you are likely to have a tiny market of interest. Especially if you hope to charge for the service at some point.

Trust me, if you can provide an accurate inventory to FOL's, that is worth paying for.