Hi Jagadeesh,
I'm not sure I understand exactly what you mean by "the reason behind selecting the image of exact kind." However, like I mentioned in the previous post, your image is a JPG file (which doesn't support transparency).
For more information of picture file types, including a description of transparency and which file types support transparency, I would suggest reading these webpages:
http://animalscience.ucdavis.edu/Intranet/Graphics/PictureFormat/default.htm
http://www.hitmill.com/html/webimages.html
Note: It looks like GIF, PNG, and TIFF are the only file types that support transparency.
Note2: You can make a GIF with transparency by creating a .psd file (with transparency) in Photoshop and then saving it as a GIF.
Hope this helps!
Travis H.
National Instruments
Travis H.
LabVIEW R&D
National Instruments