Toggling image sources
Interesting question, in that you gave away most of the answer in this function:


    function changeName(imgName) {    
       var pos = imgName.indexOf("_");
       var first = imgName.substring(0,pos);
       return first.concat("","_unselected.png");
    }



You know that all unselected images end with "_unselected.png" and by extension you know that all selected images end with "_selected.png". As a side note I would not have used indexOf, and substring, I would have used a split and string concatenation thru +:

    function deriveUnselectedVersion( imagePath ){    
       var firstPart = imagePath.split("_")[0];
       return firstPart + '_unselected.png';
    }


I am not 100% confident about deriveUnselectedVersion but it sure sounds better (and is more meaningful) than changeName.

Anyway, this is how I would write the click handler:

 $(".tt").click(function(event) {                 
       var image = event.target,
           title = image.getAttribute("title"),
           sourceInfo = image.getAttribute("src").split("_"),
           base = sourceInfo[0],
           version = sourceInfo[1];

       resetOtherImages(title);     

       if( version == "selected.png" ){
         $(this).attr('src', base + "_unselected.png");      
       } else {
         $(this).attr('src', base + "_selected.png");            
       }

       //Or we could go really (too) fancy
        $(this).attr('src', base + ( version == "selected.png" ? "_unselected.png" : "_selected.png" ) );

    });


You will notice:


No missing semi colons at the end of statements
1 var statement on top to rule them all
Only 1 $() statement executed (these are expensive)
This will work for all new buttons as long they follow the same naming scheme
Much shorter
I am still ambivalent about using var title, since title is used in only one place..


A final advice is that writing code follows the same rules as writing prose, dont repeat yourself (too much) aka DRY.

    function resetOtherImages(title) {
    $('.tt').each(function(){
        if($(this).attr('src') !== title)
        {
          var newName = changeName($(this).attr('src'))
          $(this).attr('src',newName)   
        }
    });
    }


See how many times you repeat $(this).attr('src') ? You can and should do better than that.