123D Catch is an app for Windows, OSX and Android that lets a user turn a series of photographs into a 3D model (a process known as photogrammetry).
Is there an alternative, preferably with a GUI, available for Linux/Ubuntu?
Enjoy the open source realm, you can find many such apps:
Moreover you can use a GNU/Linux distribution called ArcheOS.
ArcheOS is the acronym of Archeological Operating System. It is a GNU/Linux live distribution built for archaeological aims. At the moment a new version (5.0 codename “Theodoric”) based on Debian “Wheezy” is under development.
You can use the 3D applications that suit your needs.