Remove 'wp-content/themes/themename/' from Image path

Hello WP-Forum,
I’m currently moving an old website based on some other CMS towards a new server, with WordPress. However, the site ranks good on Google, and I’m have to keep all the link structure, including the ones from images.

So, in the old CMS, the links to images were like this:
https://www.domain-name.de/images/image1.jpg

Right now, they are like this:
https://www.domain-name.de/wp-content/themes/theme-name/images/image1.jpg

But they have to look like in the first example.

I’m using a lot the <?php bloginfo('template_url'); ?>/images/... code, so changing that in all .php files and widgets, pages and so on would take hours.

Is there anyway to achieve that with some way to do it, maybe with htaccess?

EDIT: After searching, I tried a few “Relative image paths” which I found on google… but none of them worked.
e.g. i tried this:

function relativePathForUploads($fileInfos)
{
	global $blog_id;
	$path = get_blog_option($blog_id,'siteurl');

	$fileInfos['url'] = str_replace($path,'',$fileInfos['url']);

	return $fileInfos;
}
add_filter('wp_handle_upload', 'relativePathForUploads');

and copied it into the functions.php, but it does not do anything.