Walmart's image guide sets a file cap that most sellers miss: 1MB maximum per image. Preferred format is JPEG or JPG, PNG/BMP/GIF are accepted, animated GIFs are not. Resolution is separate from weight, and the numbers are strict. For zoom capability Walmart wants 2000x2000 pixels at 300 ppi. Without zoom, the minimum is 500x500 at 72 ppi — and Walmart says outright that SKUs whose primary image falls below 500x500 get unpublished automatically, with the status reason 'An image for your item does not meet minimum required resolution of 500x500 pixels.' So the two failure modes are opposite: a 6000px camera original blows the 1MB cap, and a squeezed export trips the resolution floor and takes the listing offline. The fix is sequencing, not a magic setting. Crop the product tight to the frame, resize to 2000x2000, then compress until the readout says under 1MB — resizing first does most of the work, so the quality slider barely has to move. Skwish does resize and compression in the browser with a per-file before/after readout, a batch queue and a ZIP export. Nothing is uploaded to a server.