Most the time if the bulbils are not removed the bulbils will squeeze out the flowers. The plant will also abort the flowers in favor of bulbil development. That's why removing the bulbils is most likely necessary. True seed also takes a while to develop. After removing the bulbils the seed heads will start to swell around August(at least here in MO). Then they stay green and growing for a month or more. In September they start to dry which takes a long time. I like to put them in a paper bag and forget about them until around November when most of the seed heads have released the seed on there own. That's when I start to process it. The seeds look just like onion seeds but a bit smaller. Very rough shaped but still roundish. There tends to be be a lot bits with the chaff. I think it under developed seeds but I'm not sure. Also I last year was the first year that I tried the cut scape method. I left the scapes on the plants until late July after they had been pollinated and started swelling. I put them in water for about a month and then let them dry for a about a week before I put them in a bag. If the scapes are cut a put into water sooner it might speed up the process. I can only speak about what I have experienced.
Here's some picks from the last couple of years.
Flower head after bulbil removal 16'
After bulbil removal 15'
Swelling flower heads right after being cut 16'
True seed from 16'
Better pic of what seed looks like. This is from 15'
Hopefully it is true seed. Herd to tell form the picture. Your garlic seems to have a ton of flowers which is good and they are purple which is a great sign that it is fertile. What variety is it? I've had the best luck with chesnok red.
-Zach