we are using Icon control and icon source (External Url) to display Green tick mark.
1) When ever we create a new case then we need to send a mail to end user , In the mail sent to end user we are providing the link(click here). When user click on that link it will open new browser where we are entering credentials(user name & pwd).
2) we need to display section with tick mark.
When we login as Admin(developer) displaying as expected.
I think the issue is because the end user is not able to reach the external URL. Are both the users tested in the same environments? Can you do a trial and error with the access roles to see if any of the access roles are restricting external URL access? Before you do that check if both the users are being tested using the same browser settings.
Also, providing an external URL is not the right way of doing it. Instead as Faizan suggested, download that image to your local system. Then create a new Binary file rule and upload the image. Then you can search for this rule with the rule name from the webwb container when you configure icon to an image control which you use to confirm once the end user action is done. Hope this helps.