Normally images have to be texture-mapped onto Geos. You have to use [pix_texture] to map the current image onto a Geo. "Current" means that any pix-manipulation that is done after texturing will not be displayed.
Any Geo has a color (which is initially set to white). If you have set the color to black, your Geo (including the image) might be very dark. If you are using alpha-blending, make sure that the Geo is not invisible.
Normally images that want to be texture mapped with openGL should have dimensions that are a power of 2 in both height and width. Now [pix_texture] will make this totally transparent to you (so normally you don't have to care about the size of the image). However with non-power-of-2 images pix_coordinate might not behave as expected, because these images need absolute texture-coordinates rather than normalized ones (as are used with power-of-2 images): so if the texture-coordinates are set to "(0,0) (1,0) (1,1) (0,1)" you might see only the first pixel of the image (which might be black).
Also, make sure that GEM can find your image (ie, that the path name is correct).