The typical HTML email message doesn’t contain images itself but, rather, downloads them from a web server. So blocked images mean two things for email marketers: 1) The message can’t be counted as an “open” because this kind of tracking involves downloading a single pixel "invisible gif"; 2) None of the graphics in either the articles or the ads will appear.

Perhaps you have noticed some of the effects already in the form of lower open rates, fewer clicks on ads, or a general lack of responsiveness in campaigns that previously got people very engaged. If so, there are several courses of action to take, and you should take them simultaneously. Please read Three counter measures for image blocking.