I've been working on a gallery and, having looked at many approaches, I'm closest to what I need with the WP's own Gallery: "real" pages generated automatically with next/previous navigation included.
What I need, that I don't currently have, is the ability to use a separate full image and thumbnail files. The images I'm using have to be cropped by hand for thumbnails.
After researching gallery plugins and putting a gallery together with template tags and attachment.php, I checked with the WordPress.org forum where a moderator referred me to the image.php. For giggles, I dropped the image.php from the WP Default theme into my child theme and, yes, it threw a syntax error.
What would you recommend?