How do I resize or compress an image for free?

On a Mac, open the image in Preview: the Adjust Size tool changes its dimensions, and File > Export saves it in another format such as JPEG. On any computer, Squoosh, a free web app from Google, resizes and compresses in the browser and does not send your image to a server, which makes it safe for an ID or a signature you have to upload to a government form with a size limit. For iPhone photos that arrive as HEIC: set Settings > Camera > Formats to Most Compatible and new photos are saved as JPEG; for an existing HEIC, open it in Photos or Preview on a Mac and choose File > Export to save a JPEG, and on Windows install Microsoft's free HEIF Image Extension so the Photos app opens it. Avoid converter sites that make you wait through ads with your passport photo uploaded to them. Rule: Squoosh for anything that must fit under a size limit, Preview or the phone's own setting for HEIC.