How can I generate the name for pictures?

When I extract the odt file, I have acess to folder pictures, and if I wisher change the image name, and change the referenc in the xml content file, I have the message that file was corrupted, because the name of picture need to be a name with 40 character. How can I generate the correct name to save the image in this repository? Thanks

It is easier to change the file normally, it is not necessary to unzip, and the generation of the names of the images in the pictures folder are automatic.