It's a bit detailed.. I'll do my best to explain....

First, drag your 6 masked images to the Symbols Panel to covert them to symbols. And create a rectangle the same size as your clipping masks but no masking. You just want a standard rectangle that is the size of the masks.

I used simply 6 random objects with clipping masks. The black square is the mask size. Drag that to the Symbols panel as well.

![Symbols][1]

In your circle, set guides to indicate the center point.

Turn on Smart Guides (View > Smart Guides) and place the black rectangle symbol on the center left edge of the circle. Now, using the Line Tool or Pen Tool, draw a path from the center of the black rectangle to the center of the circle.

![Center path][2]

*(You can turn off Smart Guides now if desired. Smart Guides can slow down drawing and won't be needed for the rest of this description.)*

Select the black Symbol and the path and group them (Object > Group)

Now, choose Effect > Distort & Transform > Transform.
Click the right-center point for the 9 Point Origin box, and enter 5 for the number of copies (1 original + 5 copies = 6 objects)
In the Angle field, let Illustrator do the math. Half a circle radius = 180° and you want 5 copies. So enter 180/5 in the Angle field. That is 180 divided by 5 and illustrator will calculate the angle. This will ultimately be 36°.

Hit OK.

![Effect][3]

Now choose Object > Expand Apeparance
And choose Object > Ungroup, and Object > Ungroup again. (You need to ungroup twice.)
You can now delete the paths to the center of the circle.
This leaves you with 6 perfectly spaced black symbols around the bottom of the circle.

![black symbols][4]

Now to use your desired images... select one of the black symbols on the circle, in the Control bar, at the top of the screen, a "Replace" item will appear. Simply click that and choose the symbol you wish to replace the black symbol with.

![replace][5]

Go through clicking all the black symbols and replace them with the other symbols. And you should end up with 6 masked images all distributed along the bottom edge of the circle.

![Done][6]

I've specifically used Symbols due to the ability to simply replace them on the artboard. You don't *have* to use symbols though. If you want you can simply get to point where you've got the 6 black squares distributed on the circle, then move your other artwork in place using the black squares as guides for placement.


  [1]: https://i.sstatic.net/yIeQp.jpg
  [2]: https://i.sstatic.net/zxutb.jpg
  [3]: https://i.sstatic.net/s2A0B.png
  [4]: https://i.sstatic.net/PxObS.jpg
  [5]: https://i.sstatic.net/fOWEs.jpg
  [6]: https://i.sstatic.net/plNTA.jpg