I've felt both before. They feel pretty similar to me depending on how severe the ovulation pain is. The implantation pain was very sharp and lasted about 30 minutes (pretty long compared to others I've heard of). It felt like really bad trapped gas. Interestingly I've felt ovulation pains very similarly and the only difference was what point in my cycle I was. Normally my ovulation pains are less sharp and last much longer (hours). I've heard for other people implantation pains are very sharp and very quick (1-2 minutes). So the main difference is that ovulation pains last much longer while implantation pain happens quickly.
ETA: Both pains feel very much like gas pains so there is no real way of knowing the difference unless you *really* know your body signs well. Also ovulation is often accompanied by egg white cervical mucus (looks like egg whites coming out of your hoo ha).