It depends on whether you need to see the photo you're attaching to the CRM record instantly or not. IE Does it just needs to be referenced in the same way other attachments (such as documents) are referenced?
If you do not need to see the multiple photos from the record without downloading first and you're happy to reference them in the same way that you reference other attachments, you could add the additional photos in the Notes area of the record, or if you need classifications against those photos, create a new entity to hold photos and Categorise them using an Option Set.
The alternative, if you do need to see the photos instantly when viewing the record, is to either write some custom code and utilise the iFrame feature of the entity form which looks at a custom entity holding photos behind the scenes, or to look at an existing product such as PowerPhoto.