They'd probably make more money by having force-fed ads on their site.
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What I wonder is this: they must have bought the rights to show and resell the aerials...but are they also available to us by finding out the source and doing the same thing? Maybe even some of them were created with public funds and might be freely available.
I don't know the source of all the Historical Aerials imagery, but it includes the free NJGIN imagery in my list above. From old threads here where the owner responded, I gather some of it is hardcopy photographs that they scanned and rectified themselves. That would involve considerable time and effort, not to mention web hosting cost, etc.
If somebody here knows where to find these photographs and would like to scan and deliver them to me, I could turn them into maps.
Regarding the imagery created with public funds, for the stuff I'm aware of such as NJGIN and USGS HRO, the metadata says there are no usage restrictions. So you can download it, put it on a website and sell it if you want. In fact, Garmin and others are doing exactly that. And isn't that the point? It was created with public funds so anyone can use it for any purpose.
If you know a way for Historical Aerials to make more money, I'll bet the owner would love to hear it.