Drupal Pop-Up Image on page load
You can achieve that using the Popup On Load module.

The module allows to display a popup once after a certain delay on a page load. This fills a gap in popup modules family (Popups, Popup), which are designed to show popups only after a click on an HTML element, or to implement a complex behavior like modal dialog forms.
If you want to just display a popup after a page load, the Popup On Load module possibly fits your needs

The following are one of the module's main features. See project page for more.

Create an action for popup display, which can be easily integrated
into Rules system.

Create a default rules set for popup display.