How to activate a tab by default in CKEditor 3.x

open the file plugins/image/dialogs/image.js
and move the content of Link tab to the beginning of contents definition i.e. before 'info' tab:
you have do it carefully... for example, this piece of text:

{id:'Link',label:m.lang.link.title,padding:0,elements:[{id:'txtUrl',type:'text',label:m.lang.image.url,style:'width: 100%','default':'',setup:function(q,r){if(q==b){var s=r.getAttribute('_cke_saved_href');if(!s)s=r.getAttribute('href');this.setValue(s);}},commit:function(q,r){var s=this;if(q==b)if(s.getValue()||s.isChanged()){r.setAttribute('_cke_saved_href',decodeURI(s.getValue()));r.setAttribute('href','javascript:void(0)/*'+CKEDITOR.tools.getNextNumber()+'*/');if(s.getValue()||!m.config.image_removeLinkByEmptyURL)s.getDialog().addLink=true;}}},{type:'button',id:'browse',filebrowser:'Link:txtUrl',style:'float:right',hidden:true,label:m.lang.common.browseServer},{id:'cmbTarget',type:'select',label:m.lang.link.target,'default':'',items:[[m.lang.link.targetNotSet,''],[m.lang.link.targetNew,'_blank'],[m.lang.link.targetTop,'_top'],[m.lang.link.targetSelf,'_self'],[m.lang.link.targetParent,'_parent']],setup:function(q,r){if(q==b)this.setValue(r.getAttribute('target'));
},commit:function(q,r){if(q==b)if(this.getValue()||this.isChanged())r.setAttribute('target',this.getValue());}}]},

has to be moved to the place immediately after contents : [ and before { id : 'info'
(Note: see the comma at the end of the code above)

This solution only brings the Link tab to the beginning and it automatically gets selected and activated.

I need the Upload tab selected when the Image Dialog pops up without editing the code.

It would be great if CKEditor fired some interesting events to help with such customisations.

First I've been looking for events happening when the Image Dialog pops up.
There is an "overflow" event coming from a div (id="ImagePreviewBox") inside the dialog.

After the dialog loads, it is stored in editorinstance._.storedDialogs.
From there you can use the API to change the tab:
editorinstance._.storedDialogs.image.selectPage("Upload");

I didn't have much time to hack something nice, but here's the idea:

function uploadTab(ev){
        if(ev.element().id == 'ImagePreviewBox'){
                editor._.storedDialogs.image.selectPage("Upload");
                document.stopObserving("overflow", upTab);
        }
}
document.observe("overflow", uploadTab );

A better way would be to :
preload the image dialog inside the storedDialogs
and add a listener:

editor._.storedDialogs.image.on('show', function(){this.selectPage("Upload")});

For future reference, this HOWTO article describes how to set CKEditor to show a specific dialog window tab to open by default: http://docs.cksource.com/CKEditor_3.x/H ... Dialog_Tab