Very neat filter. I have the Eliminate White, Eliminate Black and the Whitewash filter. All three of the filters require that your image be in RGB color mode and they will only function on a layer. If your image is on the background, you must first promote it to a layer before running the filter. Eliminate White strips the active layer of white pixels. Light-colored pixels in the layer are made partially transparent based on the level of whiteness. If you find the image too transparent, you can duplicate layer 2-3 times (or however many you need) and merge down (not flatten).

Unfortunately, not all filters work in CMYK mode.