How to create custom page with user images in grid and with pagination, not using views As I guess I need to override node.tpl.php or page.tpl.php?
use hook_menu() to create a path to your page. Then use db_select() with the tableSort extender to supply pagination in the hook_menu page callback. Select the uid, username, user image(s) ? in your database query.

Then just loop over your resultset and output a div with your user images per cell. Simply float all the divs to the left so your output appears as a grid instead of a single long column of rows.