A Multi-state object (MSO) is probably the best way to have an image with a pop up version that's larger. You would add content as different states in the MSO and control which state is viewed with buttons (in this case a smaller version of the image). An MSO could contain an empty state for normal viewing and when a button (it could be an invisible button over the content you want zoomed in) is clicked, the MSO could switch to a state that contains a scaled-up version of the content and that content could be whatever magnification you set it to be. Find step-by-step instructions for making pop-ups in our free InDesign UX Design Patterns guide
You can also make a pop-up using the in5 Pop-up Builder.
The following are other options for zooming up content without using an MSO.
The Interactive Widget for Pan & Zoom - Select your image and go to in5 > Interactive Widgets > Pan & Zoom to turn this option on in the dialog that opens. When the document is exported, double-clicking on content that has been placed inside of the frame will increase it to 200%. Double-clicking again will return it to 100%.
A lightbox - Place an image, right-click, and select Mark as Thumbnail. When you export, go to in5 > Export HTML5 with in5, and in the Basic section, under Navigation, select Open Thumbnails in Lightbox. When you click on the image, a larger version opens in a lightbox.
A button with a rollover state - Scale down the image and make it a button. Add a rollover state, and scale the image back up. When you rollover the image, then the larger version appears.
Viewer Display - When you export, go to in5 > Export HTML5 with in5, and in the Viewer Display section, under Control Frame options, select Zoom in/out. That option adds the bar along the bottom of your publication with the zoom control enabled.