Merchant Center's image_link spec is generous in file size and specific in pixels. Files can be JPEG, PNG, WebP, GIF, BMP or TIFF up to 16MB, and the image can be no larger than 64 megapixels — but the floor is 500x500 and the recommendation is 1500x1500 or above, because that is what holds up across Shopping ads, free listings, high-density screens and TV surfaces. In practice merchants fail on both ends: photographers deliver 40MB TIFF masters that blow the file cap, and cheap feed apps export 400px thumbnails that get disapproved for being too small. Between those two failures sits the file that actually works: a 1500x1500 JPEG or WebP at a few hundred kilobytes, extension matching the real format, product filling 75% to 90% of the frame, no overlays or watermarks. Skwish resizes and compresses to that window in the browser with a per-file readout and a batch queue, so a catalog goes through in one pass. Nothing is uploaded to a server.