Q: Why won't my iPhone 5 send picture messages anymore?

To resolve issues with sending and receiving iMessages, follow these steps

1. Check iMessage system status for current service issues.
2. Go to Settings > Messages > Send & Receive and make sure that you registered iMessage with your phone number or Apple ID and that you selected iMessage for use. If the phone number or Apple ID isn't available for use, troubleshoot iMessage registration.
3. Open Safari and navigate to www.apple.com to verify data connectivity. If a data connection isn't available, troubleshoot cellular data or a Wi-Fi connection.
4. iMessage over cellular data might not be available while you're on a call. Only 3G and faster GSM networks support simultaneous data and voice calls. Learn which network your phone supports. If your network doesn't support simultaneous data and voice calls, go to Settings > Wi-Fi and turn Wi-Fi on to use iMessage while you're on a call.
5. Restart your device.
6. Tap Settings > General > Reset > Reset Network Settings on your iPhone.

If you still can't send or receive an iMessage, follow these steps

1. Make sure that the contact trying to message you isn't blocked in Settings > Messages > Blocked.
2. Make sure that the contact you're trying to send a message to is registered with iMessage.
3. If the issue occurs with a specific contact or contacts, back up or forward important messages and delete your current messaging threads with the contact. Create a new message to the contact and try again.
4. If the issue occurs with a specific contact or contacts, delete and recreate the contact in the Contacts app. Create a new message to the newly created contact and try again.
5. Back up and restore your device as new.

http://support.apple.com/kb/ts2755

it's strange that my iphone won't send MMS to android or windows phones....    it is causing me a major problem... imessage, whatever it is, shouldn't be required in order to simply send a message to another phone

iMessage is not required for non-iOS devices. It is for messages between iOS devices. If you are having issues with sending SMS or MMS, then you need to contact the carrier as that is a carrier function.

Thank you Anthony Hobbs, Used your solution and it worked like a charm. You are a star!

Kind regards

Actually, it's the complete opposite. iMessage is only used for messages between Apple devices. Other phones use the other type. Hint: iMessages are in blue, while the other type is green.

None of this worked for me, but then I thought of something - I'd just downloaded a picture off a website. Thats what I had originally wanted to send someone. I deleted that file and boom - I can send pictures again. It must have been a corrupted file and had impacted the ability to send ANY pics, not just the corrupted one. Delete all of your pics if you don't know which one could be the problem. Email sensitive ones you're holding onto first if you need to.

I Too had a problem but it was not sending pictures to only one person. after doing more digging I saw that that contact was linked to me. I unlinked the person and now I can resume sending pics.  I hope this helps anybody else  

Make sure you have your cellular data on. I typically would turn mine off anytime I was on WiFi, but then I started having this problem. I realized that my imessages would send, but my MMS messages would not send on WiFi alone.

Yes, as soon as i switched on the cellular data it sent with no trouble at all. Strange, even with the home WiFi on and the cellular data switched off, it would not send. I think turning on the mobile data at home as well as the WiFi is a must for mms only.

You are correct. Cellular data is necessary for MMS, since it is a carrier function. It has to have cellular data, since an MMS uses the cellular network. Wi-FI will not work.