How a photo is fitted under 50 KB
ToolGPT writes the photo as a JPEG, starting at quality 92 and stepping down to 30. It stops at the first setting that fits under your limit, so the photo keeps as much quality as 50 KB allows. The pixel size stays the same unless you ask for a smaller one.
A typical phone photo won't fit at its full size. When even quality 30 is too big, ToolGPT reports the smallest size it reached and suggests a smaller long edge. Around 800 pixels is often enough for 50 KB; ask again with that size and it tries once more. The work happens in your browser.