The above picture shows, at the left, a typically nodding (downward bent) poppy flower-bud, then at the center you see a cross-section of a poppy flower, and then, at the right, a poppy fruit. There are maybe 50 species of poppy and several are found in cultivation. The above, with its very hair stems and its large petals having black spots at the base edged with white, is the Corn Poppy, Papaver rhoeas, frequently planted in gardens. The famous Opium Poppy is a different species, Papaver somniferum.
Poppy flowers show important differences from our Standard Blossom. Our Standard Blossom has 5 sepals, but poppy flowers only have 2 or rarely 3 sepals. Our Standard Blossom has 5 petals, but poppy flowers usually but not always have 4. Our Standard Blossom has 5 stamens, but you can see in the picture above the right that poppy flowers produce dozens of stamens! That picture shows a poppy flower from above. The large yellow item in the center is the stigmatic disk, while the black, stiff-looking things are stamens.
That stigma disk is unusual in the blossom world, but it's normal for poppies. The stigma is the part of the female pistil onto which male pollen grains land and germinate. Our Standard Blossom has a stigma that branches, and that's typical. But in poppy flowers the stigmas unite in a radiating pattern and join together to form that crazy disk. When you see a disk like that, think "poppy."
At the left you see a cross-section of a poppy fruit, which is a capsule or seed pod. The radiating stigma disk lies atop the capsule. The cream-colored, oval, sandgrain-like things inside the capsule are ovules -- the future seeds.
At the right is an entire capsule. The black spots are where insects have punctured the fruit's skin and milky juice, or latex, has issued and then dried into black, crusty spots.
This is very similar to what happens with Opium Poppies. Opium Poppies have been developed over the centuries to produce larger quantities of milky latex than you see on the garden poppy fruit. When the latex on Opium Poppy pods dries, that's your opium, the source of a great deal of trouble in this world, as well as an important medicine when properly used.
In the US, Opium Poppies were declared illegal in the Opium Poppy Control Act of 1942. New generations of plants from the self-sown seed of these original poppies can still be seen in many old ornamental gardens, though. You can read a lot more about this matter by clicking here.