In case users decide to block third-party cookies in their browser, they are unable to see images that they have placed inside Connect app macros, due to disabling third-party cookies results in the removal of the cookie header for the Connect app’s requests. Therefore, supporting this use of disabling third-party cookies to render assets inside an iframe would be of value to partners and customers that use the macros.

Workaround

Cookie setting is up to users as per Atlassian Cookies & Tracking Notice > How can you opt-out?:

Depending where you live, you may also have the right to opt out of targeted advertising and/or certain third-party cookies, as described in the Privacy Policy under "Your Choices."

Each app can detect whether the third-party cookie is enabled and shows a message to describe how the user experience is impacted and suggest turning it on:

if (typeof window.localStorage === 'undefined') {
    // PROVIDE FEEDBACK TO THE USER
}