If i do a print screen( not in game )where does windows store the picturers.
By default, on a Windows computer, it should be in Documents > The Lord of the Rings Online.
It should look something like this:
"Not all those who wander are lost....some are so stubborn that they always think they're going in the right direction."
"The 4th age is the store age" - Hetweith
zipfile's reply above is correct if you are using LOTRO's screenshot keybind, but you said you were not doing so.
Assuming you are using WINDOWS+PRINTSCREEN to take a screenshot, those files are stored here:
*\Pictures\Screenshots
You'll find the Pictures folder inside your Windows account user folder with the same name as your account.