Unless the image was put inline in the email, then you can't.
It all depends on how the image is attached in the email by the sender.
There might be a 3rd party plugin that changes the behavior by adding an inline preview in the resources list.
I maintain a list of osTicket Resources on my personal web site and here on the forums that you might find useful. It includes a list of Community Plugins. Here are the two links:
https://forum.osticket.com/d/92286-resources-for-osticket
https://tmib.net/resources-for-osticket/
As a disclaimer: While many people do use 3rd Party Plugins (Also called Community Plugins) it is important to know that they have not been evaluated by, are not supported by, are not recommended by, and are not written by the Developers of osTicket. You will need to reach out to the author of the Community Plugin that you are using for support.
