The best thing to do is paint your texture on your UV layout in Photoshop (be it from photo's of lizard skin or freehand) then map this into the colour channel of your model (as this forms the basis for the colour of it's scales etc) to see if it looks ok, if it does then go back into photoshop and create a copy of the colour tecture, desaturate this so that its black and white and save this as the bump map, then map the black and white picture to the bump channel then render, you then should have the bump map and the colour map matching up for ya.

You can the adjust the bump level to suit (i.e if the bump is going in instead of out then use a - value)

Hope this helps in expalining it