Bulk Download Pictures from Messages

So unbelievably I have *never* cleared my history in SMS/iMessages/Messages. Ostensibly, I should be able to scroll up and eventually see my first text message from my first gen iPhone. This is, unsurprisingly, taking up a considerable amount of space on my phone, but a big part of why I've never cleaned it out is that it contains a tremendous number of pictures of my daughters my wife has sent me over the years. It doesn't seem like these get saved to my photo roll and there doesn't appear to be any way to bulk export them. It may be worth noting that I use desktop messages in Yosemite and it seems work well, so there may be an approach I can use from that angle. What's the best way for me to archive all the photo attachments from almost seven years of text messages?