Thumbnail
A thumbnail is a small, low-detail copy of a picture, made for previews, galleries and lists rather than for looking at up close.
What it means
Websites keep small copies of their pictures so that pages load quickly. A store makes its own: Shopify, for example, automatically creates “different sizes” of each image for different parts of a theme.1 The full-size file stays behind for the zoom view.
Supplier spreadsheets often link to those small copies instead of the originals. The picture a product page shows first is sized for the page, not for a zoom, and that is the one that gets copied. Names ending _thumb, _small or _medium give many away, and Shopify asks for image file names without those endings.2
Google’s product data specification puts it in one line: “Don’t scale up an image or submit a thumbnail”.3 A thumbnail holds no more detail however large it is drawn. The fix is the original it was made from, often reachable from the zoom view on the supplier’s product page.
Think of it like this
A stamp-sized photo on a menu is a thumbnail. It tells you which dish is which, but nobody could judge the food from it.
For example
A supplier’s image column reads FS400_thumb.jpg, a picture 160 by 160 pixels. On the supplier’s product page, the zoom view loads FS400.jpg at 1500 by 1500. The second link goes into the file and the first is dropped.
Why it matters
Not to be confused with
A thumbnail is a small file, not a small display. A store can show a full-size image small in a grid, and the zoom still has every pixel to work with. A thumbnail has nothing more to give.
Sources
- Shopify Help Center. Product media types.
- Shopify Help Center. Using CSV files to import and export products.
- Google Merchant Center Help. Product data specification.
- Google Merchant Center Help. How to fix: Image too small.
- Google Merchant Center Help. Merchant Center product data specification update 2026.