Libpcap ICMP Packet never responded to

I'm playing around with Libpcap trying to send a ping but whenever I send the requests they are never responded to, no errors given and it looks identical to a regular ping sent through the ping utility.

The left packet is sent through ping on the terminal and the right through my app. As far as I can tell the data field is optional so I don't include it, and the identifier/sequence numbers can be random, so they are randomised.

Am I missing something obvious here?

I notice you haven't validated your IP header checksum. Are you sure it is in fact correct? If it isn't the next router will silently drop the packet which is consistent with what you've seen. Wireshark should be able to validate the ip header checksum for you if you switch it on.