Is there a way to get Bing's photo of the day?

I think the best way is immitating the way they do it themselves through their AJAX calls.

They call this URL and extract the information through XML deserialization.

XML: http://www.bing.com/HPImageArchive.aspx?format=xml&idx=0&n=1&mkt=en-US

JSON: http://www.bing.com/HPImageArchive.aspx?format=js&idx=0&n=1&mkt=en-US

RSS: http://www.bing.com/HPImageArchive.aspx?format=rss&idx=0&n=1&mkt=en-US

The mkt attribute can obviously be changed to a different region than ´en-US´, but can also be opted out of entirely if you don't care about a specific region.

Note that the _1366x768.jpg suffix that is added to the image names appears to be modifiable into different resolutions (like _1920x1080.jpg for full HD and possibly others).

Here's a dump of the data as of 9/28/2013, in XML format.

<?xml version="1.0" encoding="utf-8"?>
<images>
    <image>
        <startdate>20130928</startdate>
        <fullstartdate>201309280000</fullstartdate>
        <enddate>20130929</enddate>
        <url>/az/hprichbg/rb/LakeTurkana_EN-US15976511099_1366x768.jpg</url>
        <urlBase>/az/hprichbg/rb/LakeTurkana_EN-US15976511099</urlBase>
        <copyright>Lava rock pools at the southern end of Lake Turkana, in Kenya (© Nigel Pavitt/Corbis)</copyright>
        <copyrightlink>http://www.bing.com/search?q=Lake+Turkana%2C+Kenya&amp;form=hpcapt</copyrightlink>
        <drk>1</drk>
        <top>1</top>
        <bot>1</bot>
        <hotspots>
            <hotspot>
                <desc>These are the southern reaches of a lake...</desc>
                <link>http://www.bing.com/maps/?v=2&amp;cp=2.794725~37.335197&amp;lvl=7&amp;dir=0&amp;sty=b&amp;q=Lake%20Turkana%2C%20Kenya&amp;form=hphot1</link>
                <query>That stretches for 180 miles, up into another country</query>
                <LocX>15</LocX>
                <LocY>33</LocY>
            </hotspot>
            <hotspot>
                <desc>This body of water was once called the Jade Sea.</desc>
                <link>http://www.bing.com/search?q=green+algae&amp;form=hphot2</link>
                <query>What gives the water here its sometimes vibrant hue?</query>
                <LocX>37</LocX>
                <LocY>42</LocY>
            </hotspot>
            <hotspot>
                <desc>One of the world's most powerful predators lives here.</desc>
                <link>http://www.bing.com/videos/search?q=Underwater+Croc+Cams+National+Geographic&amp;FORM=hphot3#view=detail&amp;mid=D25E1909D3514A8732C5D25E1909D3514A8732C5</link>
                <query>See some rare underwater footage of the beast</query>
                <LocX>66</LocX>
                <LocY>33</LocY>
            </hotspot>
            <hotspot>
                <desc>Many fossils of ancient human ancestors have been uncovered in the surrounding area.</desc>
                <link>http://www.bing.com/search?q=Turkana+Boy&amp;form=hphot4</link>
                <query>One skeleton was so complete, paleoanthropologists gave him a name</query>
                <LocX>82</LocX>
                <LocY>41</LocY>
            </hotspot>
        </hotspots>
        <messages></messages>
    </image>
    <tooltips>
        <loadMessage>
            <message>Indlæser...</message>
        </loadMessage>
        <previousImage>
            <text>Forrige</text>
        </previousImage>
        <nextImage>
            <text>Næste</text>
        </nextImage>
        <play>
            <text>Afspil</text>
        </play>
        <pause>
            <text>Pause</text>
        </pause>
    </tooltips>
</images>

JSON FORMAT of BING IMAGE

I found a way to fetch the JSON format of the Bing Image of the day

http://www.bing.com/HPImageArchive.aspx?format=js&idx=0&n=1

Note

      n= The no of images u want( u can use Integers) ,
      mkt= Your location (example: en-US)

  {
  "images": [
    {
      "startdate": "20141214",
      "fullstartdate": "201412141830",
      "enddate": "20141215",
      "url": "\/az\/hprichbg\/rb\/BlackButte_EN-IN7038391888_1920x1080.jpg",
      "urlbase": "\/az\/hprichbg\/rb\/BlackButte_EN-IN7038391888",
      "copyright": "Black Butte, seen from the Mount Jefferson Wilderness, Oregon, USA (\u00a9 Marc Adamus\/Aurora Photos)",
      "copyrightlink": "http:\/\/www.bing.com\/search?q=Black+Butte&qs=n&form=hpcapt&mkt=en-in&pq=black+butte&sc=8-11&sp=-1&sk=&cvid=228ac7f125f94bbaafd4a4abd4f9a32d",
      "wp": true,
      "hsh": "94156ae1e2e1be49f9b739d2b7bff65c",
      "drk": 1,
      "top": 1,
      "bot": 1,
      "hs": [

      ],
      "msg": [
        {
          "title": "How does it feel\u2026",
          "link": "http:\/\/www.bing.com\/videos\/search?q=Climbing+Black+Butte&FORM=pgbar1&mkt=en-in#view=detail&mid=58BDB2F2B9FCB85D597558BDB2F2B9FCB85D5975",
          "text": "To climb 1961.7 m?"
        },
        {
          "title": "On top of the world",
          "link": "http:\/\/www.bing.com\/images\/search?q=Pictures+From+the+Top+of+Mount+Everest&FORM=pgbar2&mkt=en-in",
          "text": "It's mountaineer's dream view"
        }
      ]
    }
  ],
  "tooltips": {
    "loading": "Loading...",
    "previous": "Previous",
    "next": "Next",
    "walle": "This image is not available to download as wallpaper.",
    "walls": "Download this image. Use of this image is restricted to wallpaper only."
  }
}

use the url from the images[]

and add it to 'http://bing.com'

here url is "url": "\/az\/hprichbg\/rb\/DayGecko_EN-US8730336235_1366x768.jpg"