Request.flickr = new Class({
    Extends: Request.JSONP,
    options: {
        callbackKey: "jsoncallback",
        url: "http://www.flickr.com/services/rest/?"
    },
    initialize: function(params, options) {
        this.parent(options);
        this.options.url = this.options.url + $H(params).toQueryString();
        
    },
    success: function(data, script) {
        this.parent(data, script);
    },
    imageURL: function(obj) {
        return "http://farm{farm}.static.flickr.com/{server}/{id}_{secret}.jpg".substitute(obj);
        
    }
});


new Request.flickr({
    format: 'json',
    api_key: "e7df6c74d2545f55414423463bf99723",
    per_page: 10,
    tags: "mountains",
    method: "flickr.photos.search"
}, {
    onSuccess: function(data) {
        target = $("action");
        data.photos.photo.each(function(el) {
            new Asset.image(this.imageURL(el), {
                onload: function() {
                    var size = this.getSize();
                    var $ar = ((this.width > this.height) ? this.width/(this.height/100)/100 : this.width / this.height).round(2);
                    // console.log(this.width, this.height, $ar);
                    this.set({
                        styles: {
                            width: 110,
                            height: 110 / $ar
                        },
                        title: this.width + "x"+ this.height + " AR: " + $ar
                    });
                    
                    this.inject(target);
                }
            });
        }, this);
    }
}).send();

<div id="action"></div>

jsFiddle