How can I add small image on top of another image in outlook to make small image as hyperlink in Outlook

Question

I'm creating a poster for an email. I have a one big image-

and one small image-

I want to put the small one on top of another and insert a hyperlink like below.

When the next person receives the mail, the position of the smaller images changes and it is visible properly only when the mail is expanded(maximized).

How do I fix this?