The image alone gives an indication as to how hard your Abs work during this movement. The exercise demonstration is shown on Dipping Bars, requiring greater control to avoid swinging (similarly to Hanging Knee Raises). Although the exercise can be performed using a Vertical Knee Raise Station, you should be mindful of anchoring momentum from the back rest in the circumstance of using a Vertical Knee Raise Station though.
Vertical Knee Raises can be made more difficult by straightening your legs, see: Vertical/ Hanging Hip Flexion.
To achieve a six pack like that shown, check out this article: How to get Six-Pack Abs.