The Multiple-Photo Texture Control section has two controls.
The ‘Perform occlusion checking’ check box determines if the texture algorithm during quality texture creation determines if another surface is between the surface being textured and the source photo under consideration. If there is a surface that obscures this part of the surface then that photo will not be used for texturing. The remaining photos that are valid source material for this part of the surface will be used instead. If there are no remaining valid photos for this part of the surface, then the surface will get the non-texture pixel color (see Preferences - Exports and Output).
The ‘Multiple-Photo Texture Blending Factor’ controls how multiple photographs are blended when a part of a surface has more than one valid source photo for texturing. This factor is based on the angle between the surface and the particular photos. When the blending factor is zero, every part of the surface will get pixel data from only one of the valid photos. The photo chosen is the one which would have the largest projected pixel (see note below). When the factor is non-zero then the photo with the smallest angle is chosen up to a threshold and then that photo is blended with other photos of similar angles. Once the factor is close to 1.0 all the valid photos will be blended together based on their angle. This gives smooth transitions between photos (photos can switch on a surface) but can cause more blurring if the photo data does not line up.
Note: what is the largest projected photo pixel on a surface? Imagine that a pixel on a photograph covers a small rectangle area - small but still a definite area. Imagine now four light rays that go from the center of the camera station position through the four corners of this pixel and out into space. When these four light rays hit a surface at a distance from the camera they will form an area (much larger than the original pixel if the camera and surface are typically separated). This is the projected area of the pixel. Two things affect this area - the distance of the camera from the surface and the angle of the surface to the camera. A good pixel for texturing is close to rectangular when projected and large. Poor pixels are small or with extreme skewed shape due to perspective.
Also note: You can use mask images to mask out portions of a photo used for photo textures. See Texture mask image name on Photo Properties.