I am not sure is it really possible. I have a gallery. But few years ago, I did not cared to make the image size on attachment page full size. You know what I mean, attachment page shows default size image (500x333). But actual image size are very large. Now my question is, I want to keep the default size attachment pages intact (because of seo), and all images on attachment page are linking to file. I want to change this linking to another page that displays full size image in a template. How can I do it ?
Shorter version : I want to change the link of image from file (on attachment page) to another page that shows full size image.