Magento – How to add a link in ui form component note

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.

Magento 2 has it's own Ui module which contains all Form elements including Checkbox, CheckboxSet, Hidden, Input, MultiSelect, Radio, Select, Textarea, Wysiwyg. but It has not a Label element.

So If you want to add a field which contains dynamic text just for visible purpose then you can use container.

uiComponent form:

<container name="note_container">
   <argument name="data" xsi:type="array">
       <item name="config" xsi:type="array">
          <item name="sortOrder" xsi:type="number">30</item>
       </item>
   </argument>
   <htmlContent name="html_content">
       <argument name="block" xsi:type="object"><VendorName>\<ModuleName>\Block\Adminhtml\<CustomClass></argument>
        </htmlContent>
 </container>

Custom Class can contains your dynamic value in html or can call custom template file:

<?php

namespace <VendorName>\<ModuleName>\Block\Adminhtml;
use Magento\Framework\View\Element\Template;

class CustomClass extends Template
{
    protected $_template = 'custom.phtml';
}

custom.phtml can contains your visible data on form.