If you're unable to send photos on Locket, here are a couple of things to check:
Make sure camera permissions are enabled
Locket needs access to your camera to take and send photos. If you've disabled camera permissions, you won't be able to send anything.
On iPhone: Go to Settings → Locket → toggle on Camera.
On Android: Go to Settings → Apps → Locket → Permissions → enable Camera.
Make sure you have at least one friend added
You need to have at least one friend added on Locket before you can send a photo. If you haven't added anyone yet, you'll need to do that first. Check out How do I add friends on Locket? for a quick walkthrough.