Can you use hook_form_alter.
UPDATE : this hook_form_alter must be put in a custom module, lets say mymodule
the location of this module will be sites/all/modules/mymodule.
In order to use dpm(), you need to install the Devel module.
Here you can have a tutorial, explaining the basics for creating a custom module.
In your case, this is going to be only .info file and a .module file.
The hook_form_alter should look like
/**
* Implements hook_form_alter().
*/
function mymodule_form_alter(&$form, $form_state, $form_id) {
drupal_set_message("Form ID is : " . $form_id);
dpm($form,'form');
}
A lot of nice snippets can be borrowed from here.
drupal forum . After that you can use dpm ($form, 'form');
And see exactly the construction.
Those forms use the Drupal 7 Form API construction mechanism. The idea would be to add '#required' => TRUE
to the corresponding image field.
I hope this helps in a way.
UPDATE: Do not forget to clear your caches(even twice) after enabling a module.
Otherwise, some hooks (but not all) will not be recognized. This problem only caused a lot of frustartion when working with Drupal.
Best regards !
Oleg