It isn't clear from your photos, so here are some things to do to investigate further.
Surface:
Rub two of them together gently-- if they feel smooth, they are imitation-- if rough, that would indicate nacre.
If you have a 10x magnifier/loupe, look closely at the surface. Imitation pearls will be coarser in appearance, real nacre very smooth. (If you have a known real pearl, or known imitation pearl, you can use them for comparison.) If you don't have a magnifier, visit a jeweler and ask to use theirs, and compare with pearls they are selling.
Shape:
The irregular shapes may indicate they are pearls, but I have some imitation pearls that have irregular shapes (to mimic real pearls.)
Overtones:
Your pearls don't have show in their overtones in your photos, and that makes me think imitation is more likely.
Drill holes:
Take a close look with a magnifier at the end pearl where the silk is broken off. Check the drill hole. If it is beveled, it's imitation.
Look into the hole to see if you can see a dividing line between the nacre and a bead inside.
Look around all the drill holes. If you see any swirly pools of nacre, that is indication they are fake.
If you see places where the nacre is eroded away, see if there is a bead underneath. That would tend to indicate a cultured pearl.