First you will have to make a "mask" so to speak with your image that you want to use. The following steps will show you one way to make a mask, but you may use any of the methods you are comfortable with.
This is the picture I am using--it is a picture I took (before knowing how to use lighting with a green screen)
For this photo, I split the channels to find the best one to make a mask. I ended up using the Cyan and I adjusted the brightness and contrast.
I finished filling in the rest of the guy by using my paintbrush in black.
The outline is now filled in.
Now make the image negative so that the guy will be white and the surrounding area will be black. Save this as a jpeg or bitmap.
Open Bryce and create a 2D Picture Object as shown in picture below.
When you click on the 2D picture object icon, a box will come up. This is where you load your picture. You will see three boxes at the top. Click on "Load" on top of the first box. It will open a box to browse your computer. Find your original picture and open it.
Now you will need to load your mask. Click on "Load" on top of the second box. You will browse your computer again and find the black and white picture you made of the original photo.
You will see in the third box that the black area of the mask in now transparent. The mask "erases" the surrounding area that you don't want around the subject.
If you click on the white/black circle above the second picture, it makes your mask negative for you and you will notice in the third box that the subject is now transparent. I like to do this in PSP (or PS if you prefer) beforehand--it is my own preference.
You do not want your subject transparent though so we will not click it.
Click the check mark (not the X) on the bottom right. You will now see a square wireframe in your Bryce scene. This is your 2D picture object.
It is not complete though from here because your object looks black when rendered; it needs a light source.
Here is what the 2D picture object would look like rendered at this point.
Create a Radial Light. It is the first yellow light. You may used any others, but I have found this is the easiest to adjust. You can play around with the others once you get used to it.
You will now have a ball wireframe in your scene.
You will now need to move the lightsource in front of the 2D picture object because it is sitting right in the middle of the object at this point. First click on Edit to get to the Edit tools. Then on the front Z handlebar of the Repositioning Tool, Click, hold and move to the left with your mouse. If you are ever unsure what tools are which, you can put your cursor over them and the name will appear at the bottom left corner of your Bryce window.
You only need to move it a little bit in front of your 2D picture object, but you can play around with the distance the more you get familiar with it.
This is what it now would look like rendered. You will notice that there are two shadows--one from the sky and one from your lightsource. Depending on how your final scene will look like, you can remove the shadow from the radial lightsource or leave it in. I will show you in the next step how to remove it.
Click the E next to your radial light to edit the light. In the Light Lab, click the orange circle next to "Cast Shadows"; this turns the shadows off. Click the check mark (not the X) in the lower right corner.
You will now see there is only one shadow in the rendered scene.
Now you will want to make the radial light Track your 2D picture so it stays next to it even if you move your 2D picture object to a different place in the scene. Next to the radial light, the fourth box down, you will click, hold and move your cursor toward your 2D picture object wireframe.
The object that you put your cursor over will turn blue. As soon as you are on your 2D picture object and it turns blue, let go of your mouse button. To untrack, all you do is click on the track box once quickly.
Now, if you move your radial light, it will stay focused on the object that you track. Here, you will notice that I moved the radial light and it twists/rotates itself so it stays tracked to the 2D picture object.
The next step is very important if you will be using any other type of picture image for material or objects! You will need to save the "material" or else it will change to the image you choose for a different object.
Click on the small arrow next to Edit. Then click on the small arrow next to "Installed" on the lower left corner of the Materials box. Then click User and then click on Add in the middle bottom of the Materials box.
Now you will type a name for this material and you can add a description for it if you wish. Click the check mark (not the X) and then click the check mark (not the X) in the Materials box. Now you are free to use a picture image texture without your 2D picture object changing.
Now you can play with the scene all you like. In this scene, I added a primitive box and used a Paint Shop Pro brick pattern as the image texture for the material and I multi-replicated the box to make a wall. I added a tree also.
Enjoy and have fun with 2D picture objects!