An image cannot be shown on the email notification & confirmation ...

... but OK when viewed at www.jotform.com

Can you tell me why and how to resolve this problem?

I have cloned your form and was able to reproduce the issue you're having. 

However, this can be solved by, updating your notifier's data table.

Then, 

You will need to use the Form Fields section on the right side of the window which represent each value of the fields on your form.

Here's the result of what I did.

I hope this helps. Let us know if you need any further assistance. Thank you. 

Your advice worked!  Thank you very much.