分别发送表格数据

The code sending the formdata is

$.ajax({
    url: 'http:///www.***/upload.php',
    data: fd,
    cache: false,
    contentType: false,
    processData: false,
    type: 'POST',
    success: function(data){
        $('#form_input')[0].reset();
        location.reload();
    }
});

That code is the code that you will want to put in a separate function. To move it elsewhere, you have to make sure it still has access to all of the variables being sent, namely, fd. fd is connected to several variables, all leading back to canvas. You say that there will only be one canvas at a time, so we can make canvas a global variable, and then getting fd from anywhere will be easy.

<script>
  //Moved to global so that sendFormStuff will see it
  var canvas = document.createElement("canvas");
  var ctx = canvas.getContext("2d");
  function ResizeMe(){
    var dataurl = null;
    var uniq = 'id' + (new Date()).getTime();
    var filesToUpload = document.getElementById('input').files;
    var file = filesToUpload[0];

    // Create an image
    var img = document.createElement("img");
    // Create a file reader
    var reader = new FileReader();
    // Set the image once loaded into file reader
    reader.onload = function(e)
    {
      img.src = e.target.result;

      img.onload = function () {

        ctx.drawImage(img, 0, 0);

        var MAX_WIDTH = 200;
        var MAX_HEIGHT = 400;
        var width = img.width;
        var height = img.height;

        if (width > height) {
          if (width > MAX_WIDTH) {
            height *= MAX_WIDTH / width;
            width = MAX_WIDTH;
          }
        } else {
          if (height > MAX_HEIGHT) {
            width *= MAX_HEIGHT / height;
            height = MAX_HEIGHT;
          }
        }
        canvas.width = width;
        canvas.height = height;
        ctx.drawImage(img, 0, 0, width, height);
      } // img.onload
    }
    function sendFormStuff() {
      var dataurl = canvas.toDataURL("image/jpeg",.2);
      var blobBin = atob(dataurl.split(',')[1]);
      var array = [];
      for(var i = 0; i < blobBin.length; i++) {
        array.push(blobBin.charCodeAt(i));
      }
      var files = new Blob([new Uint8Array(array)], {type: 'image/jpg', name: "ddd"});
      // Post the data
      var fd = new FormData();
      fd.append("image", files, uniq);
      $.ajax({
        url: 'http:///www.***/upload.php',
        data: fd,
        cache: false,
        contentType: false,
        processData: false,
        type: 'POST',
        success: function(data){
          $('#form_input')[0].reset();
          location.reload();
        }
      });
    }
    // Load files into file reader
    reader.readAsDataURL(file);
  }
</script>

So really all we did here was move the request code into a separate function, and make canvas and ctx (which you were declaring twice, btw) accessible by that function.