VLock is a feature of Julius that "Locks" the "Verticals" of the photo to be straight and vertical.
Tap the VLock button to toggle VLock on or off.
The way VLock works under the hood is by applying rotation and vertical distortion corrections. These settings are also adjustable after shooting so if you decide later you'd rather have the photo without corrections, you can set the rotation and vertical sliders to zero. (Double tap to zero any slider) You can also adjust these sliders on photos that were taken without VLock or imported into Julius to make corrections.
VLock is also useful in interiors:
Notice how the converging verticals are fixed and the room looks straight and solid. It's also useful to note that there is a small amount of cropping of the image towards the upper corners. This cropping is a tradeoff that you should consider when using VLock. It's generally an acceptable tradeoff to have a small amount of cropping in order to have perfect vertical lines.