I might recommend breaking out images into a separate table, then create a linked record field between the images table and your original table here. 

In the images table, you can create something to signify the primary image (maybe a Single-select field with different numbering options, a Checkbox field, etc.) and then in your original table, I'd create two Lookup fields to the images table: one to your attachments field that is filtered only to records that are designated primary, and another to all the attachments belonging to child image records.

these images came by filling a form it will be a lot of manual work by adding every time images and split into other table