Sorry, but you are wrong on several points:
- The French law is 70 years pma.
- Alain-Fournier is born in 1882, and was 18 years old in 1904.
- The picture was made in 1904, on Alain-Fournier's 18 birthday.
So... how old was the *photographer* when the image was taken? Let's use the exmaple from the deletion request. If the photographer was 40 in 1904 and lived to be 74 (not unreasonable), so he died in 1938, the Photo would only become PD next year (70 years *pma*). If he was only 30 when he took the image and died in 1948, it's in copyright for another 10 years. This is not taking into account the extensions of copyright given for the time of the world wars by french law -- a total of nearly 15 extra years of copyright. If the creator was killed in either war, there's even an extension of 30 years.
So, assuming PD for an image that is 100 years old means assuming the photographer lived no more than 30 years after taking the picture -- not a safe bet. For France, the situation is even worse, because of the extensions mentioned above.
I think some rule of thumb was established at some point, but I'm not sure what is was. I think 200 years would be safe, and perhaps 150 are also. but even 120 are not enough, IMHO.
Anyway... you said we accept content that is a lot less safe than this. Like what, exactly?
-- Daniel