Add custom fields to media upload + append field values to attachment <title>

attachment_fields_to_edit.php

<?php
add_filter( 'attachment_fields_to_edit', 'hip_edit_media_custom_field', 11, 2 );
add_filter( 'attachment_fields_to_save', 'hip_save_media_custom_field', 11, 2 );

function hip_edit_media_custom_field( $form_fields, $post ) {

    $form_fields['image_source'] = array(
        'label' => __( 'Bildkälla', 'ds' ),
        'input' => 'text',
        'value' => get_post_meta( $post->ID, 'image_source', true ),
        'show_in_edit' => 1,
        'show_in_modal' => 1
    );

    $form_fields['photographer'] = array(
        'label' => __( 'Fotograf', 'ds' ),
        'input' => 'text',
        'value' => get_post_meta( $post->ID, 'photographer', true ),
        'show_in_edit' => 1,
        'show_in_modal' => 1
    );
    return $form_fields;
}

function hip_save_media_custom_field( $post, $attachment ) {
    update_post_meta( $post['ID'], 'image_source', $attachment['image_source'] );
    update_post_meta( $post['ID'], 'photographer', $attachment['photographer'] );
    return $post;
}
add_filter( 'wp_get_attachment_image_attributes', 'hip_attachment_attributes', 99, 2 );
function hip_attachment_attributes( $attr, $attachment ) {

    $attr['title'][0] = $attachment->post_title;

    $image_source = get_post_meta( $attachment->ID, 'image_source', true );
    $photographer = get_post_meta( $attachment->ID, 'photographer', true );

    $attr['title'][1] = ( $image_source ) ? sprintf( __( 'Bildkälla: %s', 'ds' ), $image_source ) : "none";
    $attr['title'][2] = ( $photographer ) ? sprintf( __( 'Fotograf: %s', 'ds' ), $photographer ) : "none";

    $i = 0;
    foreach ( $attr['title'] as $item ){
        if( $item ==  "none" ) {
            unset( $attr['title'][$i] );
        }
        ++$i;
    }
    $attr['title'] = implode( " | ", $attr['title'] );

  return $attr;
}
add_filter( 'image_send_to_editor', 'hip_image_send_to_editor_add_data', 999, 8 );
function hip_image_send_to_editor_add_data( $html, $id, $caption, $title, $align, $url, $size, $alt ) {
	$html = wp_get_attachment_image( $id, $size, false, array( 'class' => 'rounded' ) );
	return $html;
}