Is there any way to determine early if hair transplant has been successful? (photos)

It can take 6 to 12 months after surgery to see results.  If you are concerned it is best to contact your doctor.

The only signs that would cause concern at this point are infection or necrosis.  With infection, you would see pus, redness, heat, and drainage.  With necrosis, you would see a large adherent black scab.  While your photo is not clear, you do not appear to have either one of these.  I agree that you just need patience.  The hair in the grafts is going to fall out soon and then begin to re-grow beginning around the 3 month mark.  We have found that individuals who have sonicated PRP with very high levels of growth factors resume growth more quickly.

Now what you need is patience. Wait it out until 8 moths possibly earlier and you should see growth by 8 months that will reach styling length.  There is no short cut for time