It can be done with Show/Hide buttons:
Here's a button created from a small version of the image (notice that it's selected in the image below):
The small button has a Show/Hide Buttons and Forms action. It's action is to make the Larger Image visible (eyeball turned on) with the small image hidden (eyeball turned off).
The large image is also turned into a button (shown below):
Notice the checkbox "Hidden Until Triggered". The large button is hidden until it's triggered by the small button. Clicking on the large image also causes a Show/Hide action which shows the Small button and hides the large button.
Select the small image and convert to a button, place the large image and convert that to a button. Edit the small button to make it show/Hide the large button. The large button will be hidden until the small button is clicked, then will hide it when clicked again.
Alternatively, you can have a separate InDesign document with all of the full-size images, add text anchors to the full size images. Convert the small images to buttons (or add invisible buttons on top of them) and tell the buttons to go to the text anchors in the other document. Combine the two documents in a book, export to interactive PDF.
Thank you!! Now one more question.. It is fully working on my pdf. I want to use this pdf of the IPad.. When I put the pdf on the ipad the image doesn't show at all? Do you know why and how I can make the image show?
Thank you again!!
Once you take it to the iPad, you are in a "gray area." A fully functioning PDF viewer for iOS has yet to be fully realized. As far as I know. There are members around who know all the particulars..
Mobile devices are a crapshoot with interactive PDF. The best PDF readers, PDF Expert and GoodReader are not free.