Where are my image and details actually stored?

The image is uploaded to Creta's own asset host, and the item's details — name, description, traits, link — are written into a metadata file beside it. The address of that file is what gets recorded on the blockchain when you mint.

The metadata file is composed on our server rather than by your browser, so what the chain points at is always a Creta address and cannot be swapped for something else after the fact.

The ownership record itself lives on Polygon and does not depend on us: the item is yours at your address whatever happens to any website.