Is the developer considered sinful if his program downloads images of women from LinkedIn, given that the program cannot distinguish between genders?

The fact that the software service does not distinguish between male and female images, or does not differentiate between what is permissible to photograph and what is not, does not mean it is forbidden. Programs that can be used for both permissible and impermissible purposes are allowed to be designed and sold, except to someone who is known to be going to use them for impermissible purposes.