File and Blob should be store as single records with out-of-line key as follow:

var file_schema = {
  stores: [
    {
      name: 'file',
      type: 'TEXT'   // data type of 'file' object store key
    }
]};
db = new ydn.db.Storage('file-test-1', file_schema);

/**
 * @param {string} url URL of the file to be retrieved 
 * @param {Function=} callback optional callback
 */
var saveImage = function(url, callback) {
  var xhr = new XMLHttpRequest();
  
  xhr.open("GET", url, true);
  xhr.responseType = "blob";
   
  xhr.addEventListener("load", function () {
    if (xhr.status === 200) {
      console.log("Image retrieved");
        
      var blob = xhr.response;
 
      // Put the received blob into IndexedDB
      db.put('file', blob, url).done(function(key) {
          console.log('Save to ', 'file:' + key);
          if (callback) {callback(key);}
        }
      );
    }
  }, false);
  xhr.send();
};

/**
 * @param {string} key the key of the image record
 */
var showImage = function(key) {
  db.get('file', key).done(function(record) {

    // Get window.URL object
    var URL = window.URL || window.webkitURL; 
    // Create ObjectURL
    var imgURL = URL.createObjectURL(record); 
    // Set img src to ObjectURL
    
    var img = document.createElement('img');
    img.setAttribute('name', url);
    img.setAttribute('src', imgURL);
    document.body.appendChild(img);
 
    // Revoking ObjectURL
    URL.revokeObjectURL(imgURL);
  }, function(e) {
    console.log(e.message || e);
  });
};

Load and save an image file

url = '/ydn-db/images/HTML5_logo_and_wordmark.png';
saveImage(url); 

Image is retrieved by

showImage(url);