As many posters already pointed out, the pictures were photoshopped because it is a problem to have untzniusdik pictures lying around.
In terms of the supposed rewriting of history – hello, I don’t think it occurred to them in a million and one years that anyone would be analyzing the pictures like this!!
Like why in the world would it occur to someone that anyone would be measuring the hems and sleeves and necklines and comparing them to old versions of the pictures and analyzing why this was done and coming to the conclusion that someone was trying to rewrite history, etc?
They simply saw an untznius picture and decided to make it more tzniusdik, period. Just as SYAG does with her textbooks. If they had thought that anyone would read into it, of course they would have left it out. But that never occurred to them.
Personally, if I were in their situation, I probably would have done the same thing, without thinking twice about it.
When I used to color in pictures for my students, it never occurred to me that there was any sheker involved, because now they will think that Helen Keller wore long sleeves. I don’t care how long Helen Keller’s sleeves are – I would just prefer that my students not see pictures of short sleeves.
If the pictures were being used to teach hilchos tznius, you’d be right. But no one is using the pictures to teach hilchos tznius. We learn hilchos tznius from the Mishna Brurah, not from pictures.