No worries. What it does is remove the tracker database and re-build it, making it synchronized and saving you the time.
Also, if you have tracker-cfg application, use the menu bar, it does the same. Don't worry, it's pretty much unbreakable and, even if it does, it can be rebuilt. It does not delete the files.
Use whatever way you want. I just figured the terminal is easier and faster.
* Go to menu
* Choose X Terminal
(a window appears that is titled X Terminal)
* type:
tracker-processes --hard reset
or
tracker-processes -r
(it's the same thing)
Now close the window and start Images or Media Player to re-build all databases.