photos in messages deleted iPhone

i have always saved all my messages and now one contact has about a years worth of texts, i have come to delete them now to free space but there are about 10 pictures but when i go back to look at them only the latest 4 show up. i have to keep pressing load earlier messages but then when i get to the old ones they just show up blank.
how can i get these back?
thanks alot
Sony Vaio E Series Windows 7