title: Image GD resize to 100px while keep the ratio
body: <p>I want to resize an image to 100px (wide, or high), while keeping its ratio and quality.<br>
  All this needs to do is open a given file, resize it and overwrite the file with the new version (keeping the filename).<br>
  It should only be able to do jpeg, gif and png files.<br>
  I'm not fussy about transparencies.</p>