To see how it works, click on the demo link from below and drag horizontally the small bar to see both images that are being compared:

Implementing this script is really easy. We just need jQuery, the Before/After script, and the two images to compare.
How to add Before/After Effect on Blogger Images
Step 1. Go to "Template" and click on the "Edit HTML" button. Once the template HTMK editor opens up, click anywhere inside the code area and press the CTRL + F keys to search for the following tag - hit Enter to find it:
Step 3. Click the "Save template" button to save your changes.
Note: if the above script doesn't work for you, add it above the