How the photo gets under 200 KB
The tool first lowers the JPG quality. If even its lowest quality is over 200 KB, as it can be for a full-size camera photo, it makes the picture smaller step by step and says so under the preview. PNG has no quality setting, so a PNG can only get smaller by losing pixels: choose JPG or WebP for a photo.
The download is a new file made in your browser from your photo. Your photo is never uploaded, and location and camera details (EXIF) are left out of the download.
KB or KiB
Here 200 KB means 200,000 bytes. Some forms count a kilobyte as 1,024 bytes; for them choose KiB in the unit menu, and the limit becomes 204,800 bytes, 4,800 bytes more. If the form does not say, keep KB: a file under 200,000 bytes passes either way.
If the form also sets a minimum or a pixel size
Open Form requirements and format and enter the smallest size the form accepts, its width and height in pixels, or both. A photo that is already smaller than the minimum needs the opposite job: increase image size in KB saves it again with less compression. Meeting the size does not mean a form will accept the photo, so check its other rules too.