These full screen textured pictures cover the entire slide area and are not meant to be seamless, tiling, or repeating. These organic pictures have been made available in both 4:3 (standard) and 16:9 (widescreen) aspect ratios. Just add them to individual slides as required, or even better — add them to the Slide Master. Typically, any picture you add has no transparency in PowerPoint but that omission is easily rectified by adding the picture as a fill for a large rectangle that covers the entire slide.
Download and use these textures to make your slides.

