Hey I tried the following:
sudo add-apt-repository ppa:linuxuprising/libpng12
sudo apt update
sudo apt install libpng12-0
I'm then able to run ITK-Snap by going to the folder where it was untarred (i.e. for me: /usr/local/itksnap-3.8.0-20190612-Linux-gcc64/bin) in the terminal with command ./itksnap
I'm not sure its the perfect fix, but I can at least use the image viewer.