Add a user avatar using wordpress Media Library.

simple-user-avatar.php

<?php if ( ! defined( 'ABSPATH' ) ) { die; } // Cannot access pages directly.

/*
* Load style & scripts
*/
function itclanbd_admin_head_scripts( $hook ) {
    $allowed = ['profile.php', 'user-new.php', 'user-edit.php'];
    if ( ! in_array( $hook, $allowed ) ) {
        return;
    }
    wp_enqueue_media();
    wp_enqueue_style('finance2sell', plugins_url('css/style.css', __FILE__), array(), null);
    wp_enqueue_script('finance2sell', plugins_url('js/scripts.js', __FILE__), array(), '1.3', true);
}
add_action( 'admin_enqueue_scripts', 'itclanbd_admin_head_scripts' );

/**
 * Create fields
 * @param $user
 */
function itclanbd_add_custom_user_profile_fields($user) {
    $itclanbd_attachment_id = (int)get_user_meta( (int)$user->ID, 'itclanbd_attachment_id', true );
    ?>
    <table class="form-table">
        <tbody>
            <tr>
                <th>
                    <label for="itclanbd-add-media"><?php _e('Avatar', 'finance2sell'); ?></label>
                </th>
                <td>
                    <input type="number" name="itclanbd_attachment_id" class="itclanbd-attachment-id" value="<?php echo $itclanbd_attachment_id; ?>" />
                    <div class="itclanbd-attachment-image">
                        <?php echo get_avatar($user->ID); ?>
                    </div>
                    <div class="wp-media-buttons">
                        <button class="button itclanbd-add-media" id="itclanbd-add-media"><?php _e('Select', 'finance2sell'); ?></button>
                        <button class="button itclanbd-remove-media"><?php _e('Remove', 'finance2sell'); ?></button>
                    </div>
                </td>
            </tr>
        </tbody>
    </table>
    <?php
}
add_action( 'show_user_profile', 'itclanbd_add_custom_user_profile_fields' );
add_action( 'edit_user_profile', 'itclanbd_add_custom_user_profile_fields' );
add_action( 'user_new_form', 'itclanbd_add_custom_user_profile_fields' );

/** 
 * Update fields
 * @param $user_id
 * @return bool
 */
function itclanbd_update_custom_user_profile($user_id) {
    if( !current_user_can('edit_user', (int)$user_id) ) return false;

    delete_user_meta( (int)$user_id, 'itclanbd_attachment_id') ; //delete meta

    if( //validate POST data
        isset($_POST['itclanbd_attachment_id'])
        && is_numeric($_POST['itclanbd_attachment_id'])
        && $_POST['itclanbd_attachment_id'] > 0
    ) {
        add_user_meta( (int)$user_id, 'itclanbd_attachment_id', (int)$_POST['itclanbd_attachment_id'] ); //add user meta
    } else {
        return false;
    }

    return true;
}
add_action('user_register', 'itclanbd_update_custom_user_profile');
add_action('profile_update', 'itclanbd_update_custom_user_profile');
//add_action( 'personal_options_update', 'itclanbd_update_custom_user_profile' );
//add_action( 'edit_user_profile_update', 'itclanbd_update_custom_user_profile' );

/**
 * @param int $attachment_id
 * @param string $size
 * @return mixed
 */
function itclanbd_get_attachment_url($attachment_id = 0, $size = 'thumbnail') {
    $image = wp_get_attachment_image_src((int)$attachment_id, $size);
    return $image[0];
}

/**
 * @param string $avatar
 * @param $id_or_email
 * @return mixed|string
 */
function itclanbd_get_new_avatar( $avatar = '', $id_or_email ) {
    $user_id = 0;

    if ( is_numeric($id_or_email) ) {
        $user_id = (int)$id_or_email;
    } else if ( is_string($id_or_email) ) {
        $user = get_user_by( 'email', $id_or_email );
        $user_id = $user->id;
    } else if ( is_object($id_or_email) ) {
        $user_id = $id_or_email->user_id;
    }
    if ( $user_id == 0 ) return $avatar;

    $itclanbd_attachment_id = (int)get_user_meta( (int)$user_id, 'itclanbd_attachment_id', true );

    if($itclanbd_attachment_id){
        $image = itclanbd_get_attachment_url((int)$itclanbd_attachment_id, 'thumbnail');
        $avatar = preg_replace('/src=("|\').*?("|\')/i', 'src="'.$image.'"', $avatar);
        $avatar = preg_replace('/srcset=("|\').*?("|\')/i', 'srcset="'.$image.'"', $avatar);
    }else{
        $avatar = preg_replace('/src=("|\').*?("|\')/i', 'src="'.esc_url( get_avatar_url( (int)$user_id ) ).'"', $avatar);
        $avatar = preg_replace('/srcset=("|\').*?("|\')/i', 'srcset="'.esc_url( get_avatar_url( (int)$user_id ) ).'"', $avatar);
    }

    return $avatar;
}
add_filter( 'get_avatar', 'itclanbd_get_new_avatar', 5, 5 );


/**
 * @param $plugin
 */
function itclanbd_redirect_after_activation( $plugin ) {
    if( $plugin == plugin_basename( __FILE__ ) ) {
        wp_redirect( admin_url('profile.php') );
        exit();
    }
}
//add_action( 'activated_plugin', 'itclanbd_redirect_after_activation' );