Change existing image attachment to custom field in databse?

Hi There
I am working on a large scale e-commerce site. I switched themes. In the old theme the product images displayed by post and uploading a gallery to the post (but not inserting it) There are about 600 products on the site. In the new theme the image displays by post and a custom field called “image”. Is there anyway I can update the database to make the current gallery image attachments into a custom field called “image”. Help is appreciated. Otherwise I will be updating 600 products manually!
Thanks.