add_action( 'user_edit_form_tag','make_uploadable_form');

function make_uploadable_form() {
    echo ' enctype="multipart/form-data"';
}

add_action( 'show_user_profile', 'UploadField' );
add_action( 'edit_user_profile', 'UploadField' );

function UploadField( $user ) {
    if ( ! current_user_can( 'edit_user' ) )
        return false;

    $pid = get_user_meta( $user->ID, 'profile_photo', true );
    $img = wp_get_attachment_image( $pid );

    if ( ! empty( $img ) )
        echo( $img );
?>

<h3>Extra profile information</h3>

<table class="form-table">
    <tr>
        <th><label for="Upload">Upload</label></th>
            <td>
                <input name="profile_photo" type="file" id="profile_photo" value="" />
            </td>
</table>

<?php
}

add_action( 'personal_options_update', 'save_user_custom' );
add_action( 'edit_user_profile_update', 'save_user_custom' );

function save_user_custom($user_id){

    if($user_id == false)
        return false;

    // If the upload field has a file in it
    if(isset($_FILES['profile_photo'])){
        if(!function_exists('wp_handle_upload'))
            require_once(ABSPATH.'wp-admin/includes/file.php');

        // Get the type of the uploaded file. This is returned as "type/extension"
        $arr_file_type = wp_check_filetype(basename($_FILES['profile_photo']['name']));
        $uploaded_file_type = $arr_file_type['type'];
        // Set an array containing a list of acceptable formats
        $allowed_file_types = array('image/jpg','image/jpeg','image/gif','image/png');
        // If the uploaded file is the right format
        if(in_array($uploaded_file_type, $allowed_file_types)) {
            // Options array for the wp_handle_upload function. 'test_upload' => false
            $upload_overrides = array( 'test_form' => false );

            // Handle the upload using WP's wp_handle_upload function. Takes the posted file and an options array
            $uploaded_file = wp_handle_upload($_FILES['profile_photo'], $upload_overrides);

            // If the wp_handle_upload call returned a local path for the image
            if(isset($uploaded_file['file'])) {

                // The wp_insert_attachment function needs the literal system path, which was passed back from wp_handle_upload
                $file_name_and_location = $uploaded_file['file'];

                // Generate a title for the image that'll be used in the media library
                $file_title_for_media_library = 'your title here';

                // Set up options array to add this file as an attachment
                $attachment = array(
                        'post_mime_type' => $uploaded_file_type,
                        'post_title' => 'Uploaded image ' . addslashes($file_title_for_media_library),
                        'post_content' => '',
                        'post_status' => 'inherit'
                );

                // Run the wp_insert_attachment function. This adds the file to the media library and generates the thumbnails. If you wanted to attch this image to a post, you could pass the post id as a third param and it'd magically happen.
                $attach_id = wp_insert_attachment( $attachment, $file_name_and_location );
                require_once(ABSPATH . "wp-admin" . '/includes/image.php');
                $attach_data = wp_generate_attachment_metadata( $attach_id, $file_name_and_location );
                wp_update_attachment_metadata($attach_id,  $attach_data);

                update_user_meta( $user_id, 'profile_photo', $attach_id );

            }
        }

    }

}