As reported July 2, 2018 on Gizmodo, Samsung Messages, the default texting app on Galaxy devices, is erroneously sending pictures stored on the devices to random contacts via SMS. This was reported by several users on current model devices, such as the Galaxy Note 8 and Galaxy S9. Reportedly, this doesn’t leave any evidence of it doing so, which means that people may be unaware that their photos were sent.
The theory is that the bug is caused by interaction between Samsung Messages and recent RCS profile updates that were rolled out by carriers, including T-Mobile.
One workaround is to revoke Samsung Messages’ ability to access storage. Another workaround is to switch to a different texting app, such as Android Messages.
Read more about it here.