So, here’s the basic idea:
I add a picture in video sequencer editor and then I add my scene in it too. So how I can define where’s in my picture is something that when blender’s object goes, it goes behind it. I know I can’t say it right because my bad english but hope you understand a bit I was asking 
You need to use the Video Sequence Editor more.
The simplest way I can think of is simply to create a copy of your picture and edit it (using Photoshop or the GIMP or somesuch). Cut out to full transparency all the parts that the 3D object can pass in front of. This will leave you with a picture that is completely transparent except for the parts that your object can pass behind. Save this picture as a PNG.
Now add your PNG as a new layer in the video sequence editor with an alpha over effect between it and the 3d object.
There are other ways of doing this…
Hope this helps.
Thanks! There is one question. I remove those parts in gimp. Can I do it just brushing with eraser? because I don’t know is it alpha 0 area or just black background? How can I make sure it is working? And when I press that save as .png there is some cursors to activate so which of them are important when doing .png pics properly? Sorry, I have known jow png works but I can’t remember which tool I used and which software. and can I make alpha area with flood fill for example…?
Using GIMP: Load your image. From the Layer menu, choose Transparency, then Add Alpha Channel.
Next, I recommend pressing Z for the ‘Select contiguous regions’ tool. Make sure you enable antialiasing. Adjust your ‘similar color’ threshold and have fun. Once you have something selected that you want to remove, just drag it out of the picture and click to drop. GIMP will show the transparency as a checkerboard of light and dark greys.
You can also use the eraser tool.
Make sure all your edges are very discrete. Any large partially transparent edge will show up ghost-like when your 3D object passes behind it. Remember: firm edges.
Save as PNG to keep your alpha channel in the image. (The actual color of the ‘transparent’ pixels hasn’t changed.)
Hope this helps.
Or, just “map/assign” your photo to a “real” object (plane?) in Blender with the UV Editor?