Some user's images of StackExchange are not displayed on my mac. Since this morning I noticed that some of the user images of this site are not displayed, both on safari and on chrome (all the "fractal" images are displayed, and alo some pictures, but others are not). Is this a problem of StackExchange or of my computer? I have OS 10.10 Yosemite, and the latest versions of safari and chrome.
The user images (avatars) are stored on various services, such as Gravatar. It is possible one or more service is either unavailable or blocked on your network.

If you use a third party advert blocker within your browser, you may find some user images are blocked. Some advert blocking software considers single-source/multi-website user images a means of tracking your activity across the Internet, and thus blocks the images from loading.