If you click open a photo capsule, to the left side of it, below the "Capsule subtitle", you can see "Display style". There's a drop-down box there where you can choose between "no border", "with border" and "thumbnail".
If you choose the "thumbnail" option, any image that you put in that photo capsule will become thumbnails. Also, you can display a photo capsule full width or float it to the right side of your hub by clicking on the arrows in the photo capsule.
This learning center guide on using the hub tool, including the photo capsule, might also be of use to you. Here's the link: https://hubpageshelp.com/content/Learning-Center-u... . Hope this helped.