A modern phone photo weighs several megabytes, while upload forms often cap files at 1 MB or even 200 KB. Add photos above and choose how to compress: by quality with a slider, or to a target size, where the converter finds the quality for you and downsizes the image if that's not enough.
JPG and WEBP are compressed right in your browser. PNG and GIF are compressed on our server by reducing the palette, so transparency survives. iPhone HEIC photos become JPGs.
If a file is already smaller than what you asked for, you get it back unchanged with a note. The compressor never makes a file bigger.