Change Image Size K2 Frontpage

Hi!
We´d like to use round images for the K2 article pictures that are shown on the homepage. The problem is that the images have the same heigth as width. But the displayed pictures on the homepage are wider that high. It is no problem to fix that with photoshop but If I use rounded corners on the overlay it shows an oval instead of a circle because of the width.

How can I change that the box has identical width and heigth?

Thanks a lot!
Simon

Could you show me your website URL? This are images generated by default category view? I suspect that you use border radius set to 50% and this will work only when the image have the same width and height. One of solutions is to force width and height via CSS but firstly I need to check this page.

You are right and I know that it is because they don´t have the same width and height.
The site is: http://mindful-coach.de/
I tried to force it but everything I tried didn´t work.

And while you are there, could you take a look at some else aswell? It is a small but strange thing:
The breadcrumb image (one module) is displayed different on different pages.
If you go to "Coaching" --> "Mindful Coaching" you see two stones on the thin breadcrumb.
If you go to "Coaching" --> "Coaching Pakete" --> "Paket 1 Achtsamkeit im Alltag", you see a thicker breadcrumb with two and a half stone. That is very strange. All pages are K2 articles and those two are even in the same category.
Thanks a lot!
Simon

I was able to fix the circle problem. I changed the css of the overlay instead of the picture size.
But the breadcrumb problem stays. Could you please take a look at it?
Thanks a lot!
Simon

The breadcrumb is a default Joomla! module and it shows the elements according to menu structure. In my opinion this one page may be assigned to more that one menu item and Joomla! always take the first connection to display breadcrumb. Please make sure that any other menu item (even from different menu) not link to the same page.