Because it is available via PPA, installing gThumb 3.2.3 on Ubuntu, Linux Mint, Elementary OS and Pear OS is easy. All you have to do is add the ppa to the system, update the local repository index and install the gthumb package. Like this:
$ sudo add-apt-repository ppa:dhor/myway
$ sudo apt-get update
$ sudo apt-get install gthumb