public void setImage(AssetManager assetManager, String imgName, boolean useAlpha){
        TextureKey key = new TextureKey(imgName, true);
        Texture2D tex = (Texture2D) assetManager.loadTexture(key);
        setTexture(assetManager, tex, useAlpha);
    }
Set the image to put on the picture.

@param assetManager The {@link AssetManager} to use to load the image.
@param imgName The image name.
@param useAlpha If true, the picture will appear transparent and allow
objects behind it to appear through. If false, the transparent
portions will be the image's color at that pixel.
jme3-core/src/main/java/com/jme3/ui/Picture.java