No. The resizer runs entirely in your browser. Your images are never sent to any server, and they disappear when you close the page.
My file is smaller than the minimum KB. What does the tool do?
It first keeps the image at the highest quality. If the file is still below the minimum, it adds a small block of empty data inside the JPG so the size meets the minimum. The picture itself does not change and the form accepts it.
How do I make a good signature image?
Sign with a black pen on plain white paper, take a clear photo in good light, then crop tightly around the signature. Keep "Clean background" on: it turns the paper pure white and makes the ink darker.