Internet Explorer has a security setting that, when enabled, prevents Outlook from displaying images with a secure URL. (Image URLs starting with "http" will display, not URLs that start with "https".)
If Outlook 2010 or 2013 displays some - but not all - images, you may need to change the setting in your Internet Explorer web browser or desktop software.
To change the setting in Internet Explorer:
- Open Internet Explorer.
- Go to Tools > Internet Options.
- Click the Advanced tab.
- Scroll down to the Security settings list, then uncheck the "Do not save encrypted pages to disk" option.
- Click OK.
Before the changes take effect, it may sometimes be necessary to clear the cache in Internet Explorer and close Outlook (File > Exit to close fully). After relaunching Outlook, send yourself another email with an image that did not display previously.