This feature would indeed be really usefull:
For instance, I just added a "world flags" icon pack in Yed... In the 247 icons I just added, it is not easy to find the right one... And I don't know each flag of the world :)
On mouse hover, the icon (png in fact) does'nt display anything...
It works fine with the original icons provided in Yed (i.e. "Network storage")
How is it possible with other icon / images... I tried to tag the IPTC metadata of my images, but did'nt worked...