UGH! Chomp is doing this too. I just emailed them. LAME!!!!!!!!!!!!!!!!
So, doing a little more digging on the Chomp app, I went to Settings>Mobile Carrier Network>MMS Network Settings>Send Size limit, set it to No limit. It has a "preserve image resolution" setting, which was already checked. Sent it to my wifes iphone 5. Of course she cant check the resolution on her iphone, so I had her send it back to me. The resolution was slightly smaller when it came back to my One. Though, this could be the iphone doing some compression on its end.
However, the picture looked fine on both units when sent and re-sent.