Google chrome rehost image extension

First, you have to get an API key. If a maximum of 50 uploads per hour is sufficient, and you don't want to register an account, get an anonymous API key.

Instead of binding a left-click event handler, which may interfere with a page, I suggest to add a contentmenu entry using the chrome.contextMenus API.

Manifest file, manifest.json:

{
  "name": "Rehost img at imgurl",
  "version": "1.0",
  "manifest_version": 2,
  "background": {"scripts":["background.js"]},
  "permissions": [
    "contextMenus",
    "http://*/*", // This permission is needed to fetch URLs
    "https://*/*"
  ]
}

Put the following code in your background script (using chrome.contextMenus.create):

// background.js
chrome.contextMenus.create({
    title: "Rehost image",
    contexts: ["image"],
    onclick: function(info) {
        // Get the image from cache:
        var x = new XMLHttpRequest();
        x.onload = function() {
            // Create a form
            var fd = new FormData();
            fd.append("image", x.response); // x.response = blob
            fd.append("key", "API KEY HERE");

            // Now, upload the image
            var y = new XMLHttpRequest();
            y.onload = function() {
                var url = JSON.parse(xhr.responseText).upload.links.imgur_page;
                // Now, do something with the new url.
            };
            y.open('POST', 'http://api.imgur.com/2/upload.json');
            y.send(fd);
        };
        x.responseType = 'blob';    // Chrome 19+
        x.open('GET', info.srcUrl); // <-- info.srcUrl = location of image
        x.send();
    }
});

You could display the URL to the user (simpliest method is prompt("Here's the URL:",url);, or use localStorage to map the previous URL to the new host and/or use the chrome.webRequest API to redirect the image requests to the new host.

Using a different web service / image host to upload the picture. http://picstore.eu/ does not provide an API, so we submit a form programatically.

// background.js
chrome.contextMenus.create({
    title: "Rehost image",
    contexts: ["image"],
    onclick: function(info) {
        // Get the image from cache:
        var x = new XMLHttpRequest();
        x.onload = function() {
            var file_name = info.srcUrl.split(/[?#]/)[0].split('/').pop();
            var fd = new FormData();
            fd.append("imgUrl", "");
            fd.append("fileName[]", file_name);
            fd.append("Search files", "Browse");
            fd.append("file[]", x.response, file_name);
            fd.append("alt[]", file_name.replace(/[-_]/g, " ").replace(/\.[^.]*$/, ""));
            //fd.append("private[0]", "1"); // "Private images.."
            //fd.append("shorturl[0]", "1"); // "Create short URLs using b54"
            fd.append("new_height[]", "");
            fd.append("new_width[]", "");
            fd.append("submit", "Upload");
            var y = new XMLHttpRequest();
            y.responseType = 'document'; // Chrome 18+ (but blob is 19+)
            y.onload = function() {
                var url = y.response.getElementById('codedirect').value;
                prompt("URL:", url);
                // Now, do something with the new url.
            };
            y.open('POST', 'http://picstore.eu/upload.php');
            y.send(fd);
        };           
        x.responseType = 'blob'; // Chrome 19+
        x.open('GET', info.srcUrl); // <-- info.srcUrl = location of image
        x.send();
    }
});