Steam requires at least five screenshots per store page, each a minimum of 1920x1080 pixels in a 16:9 ratio, and screenshots should show actual gameplay rather than concept art or marketing copy. A 4K capture straight out of a game or capture tool is a 5 to 15MB PNG, and a page carrying a dozen of those is slow for every visitor and slow for you to manage while iterating on a launch. The trick is that screenshots have a hard floor but no ceiling: you can keep 1920x1080 or go larger and still cut the bytes heavily, because the weight sits in the capture's noise and gradients, not in the pixel count. Skwish compresses and resizes images locally in your browser with a live before/after readout per file, so you verify the resolution still clears 1920x1080 while the file shrinks. Batch the whole capture set, export a ZIP. Nothing is uploaded.