The STEPCRAFT CNC comes with UCCNC machine control software, which also has a plug in that will transform a bitmap image into G Code for use with the Laser so you can laser engrave a photo or other bitmap image. However, if you wish to use the laser to cut projects out, then you need a CAM program like Vectric Cut 2D or V Carve to make the tool path for the laser to follow and then output the G Code for UCCNC to read.
To summarize:
For photos/bitmap engraving - No, you don't need additional software
For cutting - Yes, you need a CAM program like Vectric Cut 2D/V Carve