Box images of different sizes

Hello Christine Rondeau Meanwhile, I congratulate you for the very nice theme I am finding it very well! I wanted to ask your advice I have created a portal where not all dimensions of the images of the posts on the home page are identical is therefore possible .. different sizes of images of the home!?
If the theme does not allow it if I create a banner in different sizes how can I insert it between the box!?
Thanks in advance