Walmart's image rules for seller photos are one part file cap and one part resolution floor. Each image has to come in at 1MB or less, JPEG preferred, on a seamless white background at 255/255/255 RGB, with no watermarks or text overlays on the Main Image. Zoom requires 2000x2000 pixels at 300 ppi, and any SKU whose primary image falls below 500x500 gets unpublished automatically. Run that across a few hundred SKUs and the workflow problem is throughput, not tuning: doing it one file at a time through an image editor is a multi-day job, and uploading a 4GB catalog folder to a cloud compressor is a different kind of job. Skwish takes up to 20 images per batch entirely in the browser, resizes to 2000x2000 and compresses each one under the cap, shows a per-file before/after readout as it goes, and exports the whole set as a ZIP with the original file names intact. Because nothing is uploaded, unreleased products stay on your machine, which is usually the constraint that rules out the convenient cloud tools. Batch a folder, download the ZIP, upload to Seller Center.