Your first optimization run

Install from the Shopify App Store, then open Apps → Zen Image Optimizer. The app opens on Home. Nothing has been touched at this point — the app has not read a single image file yet.

Press Scan images. The scan reads the size, format and dimensions of every product and Files library image from Shopify. It downloads nothing, changes nothing and uses no quota, and it can be stopped and resumed.

When it finishes, Home shows what you are working with: images tracked, how many are worth optimizing, and the total weight you could remove.

Go to Optimize and press Run preview. Five of your own images are compressed in memory only — nothing is uploaded, nothing is written and no quota is used — and you see the real before/after for your catalogue rather than an average from someone else's.

Not enough saving? Change the Preset (Lossless, Balanced, Aggressive) in Settings and press Run preview again. Balanced is the default and is the right answer for most stores.

Still on Optimize, press Optimize images and confirm. The run page then shows live progress with before/after bytes for every image, and a reason for each one that was skipped.

You can close the tab. The run continues in the background and you can come back to it from Activity.

This is the step worth doing once, so you can stop worrying about it: open Content → Files in your Shopify admin and look at an image the run just optimized. Same file name, same URL, same media ID — smaller file. Your theme, your links and your search results never saw a change.

Open Backups and press Restore on one image. The original bytes go back to the same URL, and the optimization is credited back to your allowance if it happened in the current billing cycle. Originals are kept for 30 days; a whole run can be rolled back from its page in Activity.