Help with theme tile display

I purchased a theme (Alpine) from a theme dev and the support has expired. I’m hoping it’s something simple that someone here can help me resolve before I go and renew my support with the theme dev.

If you have a look at the link below you can see the preview images for 4 separate portfolios I’ve created. All the preview images are sized the same in the media library….1500×1000

The problem is that one of those images does not seem to be the same size as all the rest. Can anyone here see any obvious reasons or how I can fix this by simply viewing the page source?

Link to page is here. It’s under the installations section. I’ve attached a screen capture to assist. Your help is much appreciated.

Thank you

https://sandbox.digitaldieselstudio.com/blog/

https://www.dropbox.com/s/5gt37msugq9l5qy/Screenshot%202016-04-06%2014.33.19.png?dl=0