The Media Chooser form element is an alternative to the default Image form element. It relies on the native Mediabrowser JS implementation and offers much more ease to upload, delete, organise and select your images across the media folder.

It is ready to be used on the 'System -> Configuration' admin area. Just declare your frontend_type and frontend_model as below, on your system.xml file:

<frontend_type>text</frontend_type>
<frontend_model>mediachooserfield/adminhtml_system_config_mediachooser</frontend_model>

For example:

<test_field>
    <label>Test field</label>
    <frontend_type>text</frontend_type>
    <frontend_model>mediachooserfield/adminhtml_system_config_mediachooser</frontend_model>
    <sort_order>10</sort_order>
    <show_in_default>1</show_in_default>
    <show_in_website>1</show_in_website>
    <show_in_store>1</show_in_store>
</test_field>

You can also use that form element directly from your custom module admin area. However, you will need to declare that new form element on your module form class, in the _prepareForm method like:

$fieldset = $form->addFieldset('my_fieldset', array('legend'=> $this->__('Mi Fieldset')));

$fieldset->addType('mediachooser','AntoineK_MediaChooserField_Data_Form_Element_Mediachooser');

$fieldset->addField('my_media_chooser_field', 'mediachooser', array(
    'name'      => 'my_media_chooser_field',
    'label'     => $this->__('My Media Chooser Field'),
    'title'     => $this->__('My Media Chooser Field'),
));

The line $fieldset->addType('mediachooser','AntoineK_MediaChooserField_Data_Form_Element_Mediachooser'); adds a new form element type. You can then simply use the media chooser form element by entering the mediachooser type.

You will also need to include manually necessary JS/CSS files. To do so, just add <update handle="editor" /> and <update handle="adminhtml_browser_js_overload" /> inside your admin layout xml file, for example:

<adminhtml_yourmodulename_yourcontrollername_edit>
      <update handle="editor" />
      <update handle="adminhtml_browser_js_overload" />
</adminhtml_yourmodulename_yourcontrollername_edit>

The editor handle automatically includes necessary JS/CSS files such as flexuploader.js, browser.js etc... You can check what it does exactly on the app/design/adminhtml/default/default/layout/main.xml file, around the line 168 (Magento 1.7.0.2).

The adminhtml_browser_js_overload overload the insert method of Mediabrowser (browser.js) to dispatch a custom event. This event will be responsible to update the image preview and button label.

Like the System/Config method, just declare your widget type as below, on your widget.xml file:

<type>mediachooserfield/adminhtml_widget_mediachooser</type>

For example:

<test_field>
    <label>Test field</label>
    <type>mediachooserfield/adminhtml_widget_mediachooser</type>
</test_field>

Add some configuration in your own module.

The configuration for the attributes foo and bar on the product form and the attributes baz and qux in the category form is:

<?xml version="1.0"?>
<config>
    <global>
        <mediachooser>
            <catalog>
                <product>
                    <attributes>
                        <foo/>
                        <bar/>
                    </attributes>
                </product>
                <category>
                    <attributes>
                        <baz/>
                        <qux/>
                    </attributes>
                </category>
            </catalog>
        </mediachooser>
    </global>
</config>

When you select an image from the media browser, the value returned is formated like wysiwyg/yourfilename.yourfileextension. So when you will reuse that value on the frontend, you would need to prefix it with Mage::getBaseUrl('media') in order to get a working and conventional URL.

Enjoy! ;-)