VRAY Tutorials: Enabling Vray render history and Compare two Render Image
The V-Ray VFB keeps a history of previously rendered images, and lists each with a number, thumbnail, and textual details in the Render history. This history can be accessed through the H icon at the bottom of the VFB window. The Render history can be docked to the VFB (as shown below) or can float separately. In addition to keeping history, this feature can display two images in the VFB for comparison (as shown below), which is revealed via a sliding division line. History files are stored as .vrimg files in a user-specified folder.
you may compare two image after changing something like light intensity, color of object, exposure etc. and you also find in VFB previous rendered image.
