Seed detection model problem

**Description**
While doing user testing on Centaurea melitensis, I found that the seed detection model had a REALLY hard time detecting this species properly.

**Bug Summary:**




For some reason, the model had a really hard time detecting the correct number of these seeds. I had to adjust the positioning and then increase the contrast to the point where the pappus (the white fluffy part at the top) pretty much disappears.

**Steps to Reproduce:**
Load any of the images below and classify. The results in my screenshot were from the 27 species model but I don't think the seed detector has changed?

**Expected Behavior:**
Five seeds would be detected, with boxes that overlapped if necessary.

**Actual Behavior:**
Boxes either straddle multiple seeds or some seeds are missed entirely.

**Environment:**

**Commit Hash:** a427278e-28df-428f-8937-ddeeef44e72f

**OS Version:** Windows 11

**Browser Version:** Edge

**Extra Screenshots:**


 This last picture was finally detected properly, but you can see it is pretty strange-looking compared to the other ones.

**Additional Context:**
I suspect the problem is something to do with the pappus (the white feathery stuff at the top of the seeds) having low contrast to the background and not a strongly defined edge. When taking images of seeds with pappus we often use a darker background, but I worried this might mess with the results further since the model, as I understand it, was trained with light background images. On the up side, the IDs were all correct!

**Suggested Fix:** (facultatif)
[If you have an idea of how to fix the bug, describe it here.]