Quiz App Email: Images for correct and incorrect answers are showing too big.

I have the exact same issue.  I am running Office2016.  I have tried to reset the defaults however no luck.

Any other ideas

I have tested the app and noticed that images are showing fine: 

Could you please try selecting to send the default email, I mean do not mark the custom email option, only the option to send the email: 

This should send you the email with the correct images, if the issue still continues, please provide us the form, we will clone it and find if this is only with your form, since I'm not able to replicate it in a cloned form. 

We will wait for your response.