PowerPoint can open an image by hovering over a thumbnail. That way, you'll keep a nice, clean slide, but also show your audience more information if you want.
To get a larger image when hovering over a thumbnail
There are four thumbnails in this example, and we want to set up a hover effect that displays a popup of a larger image when you move the mouse over Move the mouse over the individual thumbnails.
On a new slide, paste your thumbnail first by clicking Insert> Images. The preview image is any small image that you want to use as a preview image on your slide ̵
Here is an example of our slide with four inserted thumbnails.
Next, for the larger images, you'll need to add a new slide for each popup. Right-click the thumbnail of your first slide and choose New Slide. Repeat this step for any additional slides needed for each of your larger images.
In this example, we added four new slides.
Next, create the first popup. On Slide 2, delete any wildcards that were added when you inserted the new slide. To delete a placeholder, right-click on the edge of the placeholder, and then click Cut. You can also select the placeholder and then press the Delete key.
Next, add the large version of your first image (for your first popup). If there is a placeholder on your slide, click the Pictures icon to insert a picture. If your new slide does not contain a placeholder, you can also click Images on the Insert tab.
Select the larger image version of the thumbnail, and then click "Paste" 
After inserting the image, adjust the size of the image on the slide as needed on.
Next, add a border to the image. Double-click the image to activate the Format tab. On the Format tab, click the border of your choice. In this example we use the option "Simple border, white".
Repeat the steps to add a large version of all the other thumbnails used. Here we have added all four larger images for our example.
Now return to the slide with your thumbnails and click to select the first thumbnail. To create the pop-up image effect, add an action to the thumbnail. On the Insert tab, click Action.
In the Action Settings dialog box, click the Mouse Over tab. Select "Hyperlink to:" and then the slide with the larger thumbnail image (in our case Slide 2). Click "OK" when you're done.
Repeat the same steps for all other thumbnails by hovering over the appropriate slide that contains the larger image.
To view On the Slideshow tab, click From Current Slide, or press Shift + F5 on your keyboard.
Hovering over the first thumbnail will bring up a larger image. Note, however, that there is no way to return to the thumbnails. You must press the Esc key to return.