Email Insights opens are recorded several ways. For example, when a 1 by 1 tracking pixel is included in your template, the pixel detects an "open" for your campaign each time it is rendered.
The tracking code records opens each time you preview your template in Acoustic Campaign. It also records all test emails that are sent and opened, as well as any time the 'Click to View in Browser' link is selected in your email.
If you run a preview test in Email Insights by using a template that has the tracking code, all of the device previews count as opens.
Email Insight Analytics reports opens as Total opens. This means multiple opens by the same person, or multiple opens can be collected if that person reloaded images in the preview pane and later by using the browser view. In addition, Email Insights reports all the hits, even if they happen in less than one second. For example, the contact's email client can make several calls to load the image in the email after the initial open, either because of bug on their end or in order to ensure that the graphics load quickly. To get the most accurate representation of legitimate opens, it's best to do all of your testing and previews before you create the campaign in Email Insights.