Ok - I've thought that I've done this in one of my projects but it seems that I had the idea of this some times ago. I will make a little update of this component this evening with the wanted feature ;)
I've updated the component ... check it out ;)
By defining a data-dash "data-retina" to the image-tag you can define the image of the mouseover effect. But keep in mind that the mouseover image should have the same ratio/dimensions as the preview image.
Hope to helped you - might it be possible to show the final implementation of it in your project?
Thank you so much Denis. i have to say that your code was so well written, I decided to give it a try and it worked! Now I will mix the two things, but there is something I must leave because your retina will work in a gallery that has some weird controls and behaviours. Anyway I must say that I have been impressed by your talent and your kindness. I will send the link to my new site as soon as I will publish it. Luca