original book marklet :
javascript:function%20aEv(e,ev,f,c){c=(c)?c:false;if(e.addEventListener){e.addEventListener(ev,f,c)}else%20if(e.attachEvent){e.attachEvent("on"+ev,f)}else{e["on"+ev]=f}}var%20a=[[/45cat\./,/-s\.jpg/i,/-s\.jpg/gi,".jpg"],[/45cat\./,/-s\.png/i,/-s\.png/gi,".png"],[/allmusic\./,/\/JPG_\d{3}\//i,/\/JPG_\d{3}\//gi,"/JPG_1080/"],[/amazon\./,/\._[A-Z]{2}\d{3}_[\w_,-]*\.jpg/i,/\._[A-Z]{2}\d{3}_[\w_,-]*\.jpg/gi,".jpg"],[/amazon\./,/\._[A-Z]{2}\d{3}_[\w_,-]*\.png/i,/\._[A-Z]{2}\d{3}_[\w_,-]*\.png/gi,".png"],[/bandcamp\./,/_\d\.jpg/i,/_\d\.jpg/gi,"_0.jpg"],[/bandcamp\./,/_\d\.png/i,/_\d\.png/gi,"_0.png"],[/cdbaby\./,/images\..*_small\.[jpgpng]{3}/i,/_small\./gi,"."],[/cdbaby\./,/images\..*\.jpg/i,/\.jpg/gi,"_large.jpg"],[/cdbaby\./,/images\..*\.png/i,/\.png/gi,"_large.png"],[/itunes\.apple\./,/1\d0x1\d0-75\./i,/1\d0x1\d0-75\./gi,"1200x1200-75."],[/jamendo\./,/1\.\d00\.jpg/i,/1\.\d00\.jpg/gi,"1.0.jpg"],[/jamendo\./,/1\.\d00\.png/i,/1\.\d00\.png/gi,"1.0.png"],[/last(fm)?\.[a-z]{2,3}/,/\/serve\/\d{3}[^\/]*\//i,/\/serve\/\d{3}[^\/]*\//gi,"/serve/_/"],[/magnatune\./,/cover_\d{2,3}\./i,/cover_\d{2,3}\./gi,"cover."],[/musicbrainz\.org/,/_thumb\d{3}\./i,/_thumb\d{3}\./gi,"."],[/musicbrainz\.org/,/-\d{3}\.jpg/i,/-\d{3}\.jpg/gi,".jpg"],[/musicbrainz\.org/,/-\d{3}\.png/i,/-\d{3}\.png/gi,".png"],[/musicdiner\./,/1\d0x1\d0-75\./i,/1\d0x1\d0-75\./gi,"1200x1200-75."],[/soundcloud\./,/t\d\d0x\d\d0\./i,/t\d\d0x\d\d0\./gi,"original."],[/play\.google\.com/,/googleusercontent\.com.*\=w\d{3}/,/\=w\d{3}$/,"=w1200"]];var%20w=null,n=0,m=20,d=document;if(d.location.hostname.search(/soundcloud\./)>-1){spans=document.querySelectorAll("span[style*=background-image]");for(i=0;i<spans.length;i++){if(spans[i].style.backgroundImage){imgsrc=spans[i].style.backgroundImage.match(/url[\(\"\u0027]+([^\"\u0027\)]*)[\)\"\u0027]+/)[1];if((spans[i].getElementsByTagName("img").length==0)&&(imgsrc.match(/t[\d]{3}x[\d]{3}\./)!=null))spans[i].innerHTML="<img%20src=\u0027"+imgsrc+"\u0027%20alt=\u0027\u0027%20style=\u0027width:50px;height:50px;border:none\u0027%20/>";}}}o:for(var%20v=0;v<a.length;v++)if(d.location.hostname.search(a[v][0])>-1){w=a[v];var%20l=d.getElementsByTagName("img");if(l)for(var%20i=0;i<l.length;i++){if((l[i].src).search(w[1])>-1){l[i].style.border="1px%20#FB0%20solid";if(l[i].naturalWidth)l[i].onmouseover=function(){this.title=""+this.naturalWidth+"x"+this.naturalHeight};aEv(l[i],"load",function(){if(this.style){this.style.borderColor="#F00";if(this.naturalWidth%20&&%20this.naturalWidth>999)this.style.borderWidth="2px"}});aEv(l[i],"click",function(){if(this.src)location=this.src});l[i].src=l[i].src.replace(w[2],w[3]);n++;if(n==m)if(confirm(""+n+"%20images%20requested.%20Continue?"))m=m+20;else%20break%20o;}};};if(w==null)self.open("http://rockland.dk/BCA?v=2.01","BCA");void(0);

After javascript beautifier:

javascript: function aEv(e, ev, f, c) {
    c = (c) ? c : false;
    if (e.addEventListener) {
        e.addEventListener(ev, f, c)
    } else if (e.attachEvent) {
        e.attachEvent("on" + ev, f)
    } else {
        e["on" + ev] = f
    }
}
var a = [
    [/45cat\./, /-s\.jpg/i, /-s\.jpg/gi, ".jpg"],
    [/45cat\./, /-s\.png/i, /-s\.png/gi, ".png"],
    [/allmusic\./, /\/JPG_\d{3}\//i, /\/JPG_\d{3}\//gi, "/JPG_1080/"],
    [/amazon\./, /\._[A-Z]{2}\d{3}_[\w_,-]*\.jpg/i, /\._[A-Z]{2}\d{3}_[\w_,-]*\.jpg/gi, ".jpg"],
    [/amazon\./, /\._[A-Z]{2}\d{3}_[\w_,-]*\.png/i, /\._[A-Z]{2}\d{3}_[\w_,-]*\.png/gi, ".png"],
    [/bandcamp\./, /_\d\.jpg/i, /_\d\.jpg/gi, "_0.jpg"],
    [/bandcamp\./, /_\d\.png/i, /_\d\.png/gi, "_0.png"],
    [/cdbaby\./, /images\..*_small\.[jpgpng]{3}/i, /_small\./gi, "."],
    [/cdbaby\./, /images\..*\.jpg/i, /\.jpg/gi, "_large.jpg"],
    [/cdbaby\./, /images\..*\.png/i, /\.png/gi, "_large.png"],
    [/itunes\.apple\./, /1\d0x1\d0-75\./i, /1\d0x1\d0-75\./gi, "1200x1200-75."],
    [/jamendo\./, /1\.\d00\.jpg/i, /1\.\d00\.jpg/gi, "1.0.jpg"],
    [/jamendo\./, /1\.\d00\.png/i, /1\.\d00\.png/gi, "1.0.png"],
    [/last(fm)?\.[a-z]{2,3}/, /\/serve\/\d{3}[^\/]*\//i, /\/serve\/\d{3}[^\/]*\//gi, "/serve/_/"],
    [/magnatune\./, /cover_\d{2,3}\./i, /cover_\d{2,3}\./gi, "cover."],
    [/musicbrainz\.org/, /_thumb\d{3}\./i, /_thumb\d{3}\./gi, "."],
    [/musicbrainz\.org/, /-\d{3}\.jpg/i, /-\d{3}\.jpg/gi, ".jpg"],
    [/musicbrainz\.org/, /-\d{3}\.png/i, /-\d{3}\.png/gi, ".png"],
    [/musicdiner\./, /1\d0x1\d0-75\./i, /1\d0x1\d0-75\./gi, "1200x1200-75."],
    [/soundcloud\./, /t\d\d0x\d\d0\./i, /t\d\d0x\d\d0\./gi, "original."],
    [/play\.google\.com/, /googleusercontent\.com.*\=w\d{3}/, /\=w\d{3}$/, "=w1200"]
];
var w = null,
    n = 0,
    m = 20,
    d = document;
if (d.location.hostname.search(/soundcloud\./) > -1) {
    spans = document.querySelectorAll("span[style*=background-image]");
    for (i = 0; i < spans.length; i++) {
        if (spans[i].style.backgroundImage) {
            imgsrc = spans[i].style.backgroundImage.match(/url[\(\"\u0027]+([^\"\u0027\)]*)[\)\"\u0027]+/)[1];
            if ((spans[i].getElementsByTagName("img").length == 0) && (imgsrc.match(/t[\d]{3}x[\d]{3}\./) != null)) spans[i].innerHTML = "<img src=\u0027" + imgsrc + "\u0027 alt=\u0027\u0027 style=\u0027width:50px;height:50px;border:none\u0027 />";
        }
    }
}
o: for (var v = 0; v < a.length; v++)
    if (d.location.hostname.search(a[v][0]) > -1) {
        w = a[v];
        var l = d.getElementsByTagName("img");
        if (l)
            for (var i = 0; i < l.length; i++) {
                if ((l[i].src).search(w[1]) > -1) {
                    l[i].style.border = "1px #FB0 solid";
                    if (l[i].naturalWidth) l[i].onmouseover = function() {
                        this.title = "" + this.naturalWidth + "x" + this.naturalHeight
                    };
                    aEv(l[i], "load", function() {
                        if (this.style) {
                            this.style.borderColor = "#F00";
                            if (this.naturalWidth && this.naturalWidth > 999) this.style.borderWidth = "2px"
                        }
                    });
                    aEv(l[i], "click", function() {
                        if (this.src) location = this.src
                    });
                    l[i].src = l[i].src.replace(w[2], w[3]);
                    n++;
                    if (n == m)
                        if (confirm("" + n + " images requested. Continue?")) m = m + 20;
                        else break o;
                }
            };
    };
if (w == null) self.open("http://rockland.dk/BCA?v=2.01", "BCA");
void(0);