Ledsteplin
Ambassador
Changing the setting to "Download and Keep" didn't fix this for me.
What, exactly, happens when you try to send a photo? Are they iMessage or MMS? Or both? Do you have MMS enabled in Settings >Messages? If not, toggle it on.
Also try swiping the messages app out of multitasking.
Try Reset Network Settings.
Reset Network Settings Settings>General>Reset>Tap Reset Network Settings. You may need to enter your wifi passcode back in afterwards.
Keep in mind photos won't send on cellular in a metal building.