faisalm88,
Are you using the 2D version of this function?
http://zone.ni.com/reference/en-XX/help/372656C-01/lvwavelettk/wa_discrete_wavelet_transform/
I've never used it myself nor am I knowledgeable in Wavelet Transform, but I'm assuming you'd have to flatten your image to a DBL 2D array, then pass it in.
If you're using this already, are you running into some kind of issue with the output?