Most email clients only display images if you click an option to display images or 'trust the sender'.

If the user has previously selected never to display images then this will have to be unset to get back the option to display images.

Each email client has a different way of enabling images to display. There are many articles on the internet about this topic for example:

How do I enable my client to display images?:

In Once Setup, Edit Quote Template, you can include both your business logo and business name or set an empty entry for either of them.

We recommend always including your business name so the Quote/Invoice has your business name clearly displayed even if the logo is excluded by the email client.