This is not a technology problem, its a process problem. Vast majority of submitters could be cheaply verified and for small number of potential spammers, there are several options:
1. Require submitter to be legally traceable and identifiable. Establish fines/fees for misuse of your property and charge their bank accounts for cleaning fees. Blacklist them for life.
2. Once a submitter is identifiable and legally traceable, charge exponentially higher fees for number of submissions unless they want to show up as chain business in which case charge reasonable fee for validation and background checks.
3. Detect and avoid autonomous mass submissions except for highly trusted entities such as big chains.
1. Require submitter to be legally traceable and identifiable. Establish fines/fees for misuse of your property and charge their bank accounts for cleaning fees. Blacklist them for life.
2. Once a submitter is identifiable and legally traceable, charge exponentially higher fees for number of submissions unless they want to show up as chain business in which case charge reasonable fee for validation and background checks.
3. Detect and avoid autonomous mass submissions except for highly trusted entities such as big chains.