Has my hair transplant failed, it was done 7 months ago? (photo)

It does look like growth is slow and highly worrisome.  The average person gets 80% of the growth in 8 months to styling length to about 3 inches. It varies with individuals, some people grow their hair earlier and some later. You should wait another month and if you do not see much more growth, go back and meet with your surgeon. I see what appears to be reasonably good growth in the hairline area so that makes the remaining area behind the hairline even more worrisome.