<?php
class Page extends SiteTree {

    private static $db = array(
    );

    private static $has_one = array(
        'Photo' => 'Image'
    );

    public function getCMSFields() {
        $fields = parent::getCMSFields();

        $fields->addFieldToTab('Root.Images', $photo = UploadField::create('Photo'));

        $photo->getValidator()->setAllowedExtensions(['png','gif','jpg','jpeg']);
        $photo->setFolderName('page-headers');

        return $fields;
    }

    public function HeaderImage(){
        if($this->Photo()->exists()){
            echo "I have an image<br>";
            return $this->Photo();
        }else{
            echo "I don't have an image.<br>";
            return $this->getParentImage( $this );
        }
    }
    private function getParentImage( Page $page ){
        $parent = $page->Parent;
        if($parent->Photo()->exists()){
            return $parent->Photo();
        }elseif( $parent ){
            return $this->getParentImage( $parent );
        }
        return null;
    }

}
class Page_Controller extends ContentController {

    /**
     * An array of actions that can be accessed via a request. Each array element should be an action name, and the
     * permissions or conditions required to allow the user to access it.
     *
     * <code>
     * array (
     *     'action', // anyone can access this action
     *     'action' => true, // same as above
     *     'action' => 'ADMIN', // you must have ADMIN permissions to access this action
     *     'action' => '->checkAction' // you can only access this action if $this->checkAction() returns true
     * );
     * </code>
     *
     * @var array
     */
    private static $allowed_actions = array (
    );

    public function init() {
        parent::init();
        // You can include any CSS or JS required by your project here.
        // See: http://doc.silverstripe.org/framework/en/reference/requirements
    }

}
=======================
<div style="width: 100%; margin: 0px auto;">
    <div style="margin: 0px auto;">
        <% if $Photo %>
        <h2>This is my photo. It's 1900X300</h2>
        $Photo.CroppedImage(1900,300)
        <% else %>
        <h2>I do not have an image.</h2>
        <% end_if %>
        <% if $HeaderImage %>
        <h2>This is my header image. It's 1900X300</h2>
        $HeaderImage.CroppedImage(1900,300)
        <% else %>
        <h2>I do not have an image.</h2>
        <% end_if %>
    </div>
</div>