> Maybe there's some slight doubt in whether or not the image could be a hash collision, which depends on the hash method. It may be incredibly unlikely (near impossible?) for any hash collision depending on the specific hash strategy.
If it was a cryptographic hash (apparently not), this mathematical near-certainty is necessary but not sufficient. Like cryptography used for confidentiality or integrity, the math doesn't at all guarantee the outcome; the implementation is the most important factor.
Each entry in the illegal hash database, for example, relies on some person characterizing the original image as illegal - there is no mathematical formula for defining illegal images - and that characterization could be inaccurate. It also relies on the database's integrity, the user's application and its implementation, even the hash calculator. People on HN can imagine lots of things that could go wrong.
If I were a judge, I'd just want to know if someone witnessed CP or not. It might be unpleasant but we're talking about arresting someone for CP, which even sans conviction can be highly traumatic (including time in jail, waiting for bail or trial, as a ~child molestor) and destroy people's lives and reputations. Do you fancy appearing at a bail hearing about your CP charge, even if you are innocent? 'Kids, I have something to tell you ...'; 'Boss, I can't work for a couple weeks because ...'.
If it was a cryptographic hash (apparently not), this mathematical near-certainty is necessary but not sufficient. Like cryptography used for confidentiality or integrity, the math doesn't at all guarantee the outcome; the implementation is the most important factor.
Each entry in the illegal hash database, for example, relies on some person characterizing the original image as illegal - there is no mathematical formula for defining illegal images - and that characterization could be inaccurate. It also relies on the database's integrity, the user's application and its implementation, even the hash calculator. People on HN can imagine lots of things that could go wrong.
If I were a judge, I'd just want to know if someone witnessed CP or not. It might be unpleasant but we're talking about arresting someone for CP, which even sans conviction can be highly traumatic (including time in jail, waiting for bail or trial, as a ~child molestor) and destroy people's lives and reputations. Do you fancy appearing at a bail hearing about your CP charge, even if you are innocent? 'Kids, I have something to tell you ...'; 'Boss, I can't work for a couple weeks because ...'.