It is not safe to assume pictures are PD after 100 years. It is not safe because a general statistic about the life expectancy of the total population is just that: general. It for example includes the high child mortality of that time. Four people, two getting 10 years old, two getting 90 years old, the average is 50 years. Who of those four will have created material that fits the scope of Commons? Everything those two 90 year old people did before they got 60, will get into public domain too early with a 100-year-rule.
At the village pump I have published a small statistic based on all people who died 1907 and have an article at German Wikipedia. 75% of those people got over Yanns 55 years (56 and higher). For two of them a 100-year-rule would mean, that their first pictures/books would have been put into PD by us 34 years after their death (but luckily we did know their lifedates, so it did not happen).
Sorry but that is not acceptable. Just because we would like to put their works under public domain we can't expect them to be dead within 30 years after they did that work. This is life and not some general statistic. And life is not safe or easy to assume. You are dealing with people and their rights and that does not give you the right to create your own rules based on some general number.
Cecil
For checking it yourself, the total list of people: http://www.biketraveler.net/urs/1907.htm
Villagepump-entry: http://commons.wikimedia.org/w/index.php?title=Commons%3AVillage_pump&diff=11678687&oldid=11678360