lxde-icon-theme software package provides LXDE standard icon theme, you can install in your Ubuntu 14.04 LTS (Trusty Tahr) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install lxde-icon-theme
lxde-icon-theme is installed in your system.
Make ensure the lxde-icon-theme package were installed using the commands given below,
$ sudo dpkg-query -l | grep lxde-icon-theme *
You will get with lxde-icon-theme package name, version, architecture and description in a table
| Distro | Ubuntu 14 04 lts trusty tahr |
| Section | X Window System software |
| Package | lxde-icon-theme |
| Version | 0.5.0-1 |
| Description | LXDE standard icon theme |
| Sub Section | x11 |