Are they models in the form of .3ds or obj or something like that or are they a texture like .bmp, .jpg, .tiff?
If they're a texture, which I'm assuming, then the easiest way (although someone will probably need to correct me on at least one part) is to create a plane object (right click in the node network. Create Object/Plane), change the center so it's just in front of the camera and change the Edge vector a so the middle box is 90 and the other boxes you'll need to fiddle with so the plane is pointed towards the camera.
Next you need to make it transparent. This is the point where someone may have a better method, but the way I know is to create a water shader as the main surface shader for the plane. To do this click on the little button with the green cross to the side of the surface shader option, this is all still in the plane settings. You'll get a drop-down list with an option to create new shader. go to that then other surface shader/water shader. Now click the green cross button again and click go to "water shader 01".
Now in here set every value to 0 with the exception of the following options.
Transparency = 1
Decay distance ~=1e+010
Decay tint = 1 and needs to be set to white colour
volume 1 density. I made it completely transparent with the value 0.00976563 but it may be different for each scene depending on the lighting.
volume 1 colour = 1 and needs to be set to white colour
seed = leave default
Once that's done, right click on the Plane object in the node network and go to internal network. Right click in the grey space of the node network and select create shader/colour shader/image map shader.
This will open up a folder dialog for you to find the texture you want to apply (the petal one). Find it and double click it. This will create the image map shader. Now find the arrowhead pointing out of the bottom of the water shader and drag the mouse to connect the arrowhead to the first arrowhead on the top of the image map shader. Once you've done that do the same with the arrowhead on the imagemap shader. Connect it to the arrowhead at the bottom of the node network where it says surface shader.
That's it. Seems like a lot but I just used a lot of words to describe it thoroughly. If you can't get a grasp on it then feel free to use the attached clip file. All you'll have to do is put in your texture and move the plane where you want it.
