Sorry you're having this problem laestrella.
Despite almost fixing the issue with Outlook 2013, Microsoft chose to continue using a renderer from Word to display the HTML mail, rather than an engine from Internet Explorer or the Mail app. There has been lots of discussion about this, and Microsoft probably intended to make this change, but did not. Maybe next time.
Email authors who are aware of this have workarounds, but many don't use them, because Outlook should, well, just work.
Refreshing or re-opening should eventually bring those missing pictures in. Sometimes, when opening mail which just arrived, Outlook needs just a few more seconds to fetch the pictures via the Exchange Server.
I just got used to it. But you can use
Mozilla Thunderbird or other 3rd party clients, also. Mozilla, in particular, has a great HTML renderer, since Web browsing is their forte.