Magento – Magento 2 : Add Date Picker in 24 Hour Format in Admin Form

For adding image field, you can try using plugin and always try to avoid overwrite whole class.

Vendor/Module/etc/adminhtml/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\User\Block\User\Edit\Tab\Main">
        <plugin name="sr_stackexchange_user_form" type="Vendor\Module\Plugin\Block\Adminhtml\User\Edit\Tab\Main" sortOrder="1"/>
    </type>
</config>

Vendor/Module/Plugin/Block/Adminhtml/User/Edit/Tab/Main.php

namespace Vendor\Module\Plugin\Block\Adminhtml\User\Edit\Tab;

class Main
{
    /**
     * Get form HTML
     *
     * @return string
     */
    public function aroundGetFormHtml(
        \Magento\User\Block\User\Edit\Tab\Main $subject,
        \Closure $proceed
    )
    {
        $form = $subject->getForm();
        if (is_object($form)) {
            $fieldset = $form->addFieldset('admin_user_image', ['legend' => __('User Image')]);
            $fieldset->addField(
                'user_image',
                'image',
                [
                    'name' => 'user_image',
                    'label' => __('Image'),
                    'id' => 'user_image',
                    'title' => __('Image'),
                    'required' => false,
                    'note' => 'Allow image type: jpg, jpeg, png'
                ]
            );

            $subject->setForm($form);
        }

        return $proceed();
    }
}

Clear cache.

To make your code working you have to write below code in your ".js" file.

ko.bindingHandlers.datepicker = {
            init: function(element, valueAccessor, allBindingsAccessor) {
                var $el = $(element);

                //initialize datepicker with some optional options
                var options = allBindingsAccessor().datepickerOptions || {};
                $el.datepicker(options);

                //handle the field changing
                ko.utils.registerEventHandler(element, "change", function() {
                    var observable = valueAccessor();
                    observable($el.datepicker("getDate"));
                });

                //handle disposal (if KO removes by the template binding)
                ko.utils.domNodeDisposal.addDisposeCallback(element, function() {
                    $el.datepicker("destroy");
                });

            },
            update: function(element, valueAccessor) {
                var value = ko.utils.unwrapObservable(valueAccessor()),
                    $el = $(element),
                    current = $el.datepicker("getDate");

                if (value - current !== 0) {
                    $el.datepicker("setDate", value);   
                }
            }
        };

return Component.extend({
//....
dob: ko.observable(new Date())
//....
});

Reference from: http://jsfiddle.net/rniemeyer/NAgNV/