Boat Trader listings run on BoatWizard, the Boats Group dealer tool that also feeds YachtWorld and boats.com. Its photo rules are published and unambiguous: JPG, PNG or HEIC accepted, no photo over 15 MB, no listing totalling more than 50 MB across all photos, 2160x1440 at 3:2 recommended, 1080x720 at 3:2 as the minimum, and anything under 1000 pixels on the long side explicitly rated low quality. The 50 MB combined cap is the one that surprises people. A walkthrough with engine bay, helm, cabin, head, hull sides and deck hardware easily runs 30-40 shots, and a modern phone camera at 6-9 MB each puts that set at 250 MB plus — a listing that cannot be saved, even though no single photo is over the per-file limit. The fix is not one aggressive pass. Crop to 3:2, resize to 2160x1440, and a saltwater deck shot lands around 2-4 MB with the hardware detail intact; forty of those fit the 50 MB cap with room to spare. Skwish resizes and compresses both in the browser with a running per-file readout and a batch queue, so you can see the total before you upload. Nothing leaves your machine.