The profile picture you posted depicts a Mk IVF, with the belly back of 4 .303 machine guns installed in the bomb bay. The engines also have the tropical Vokes air filters installed, visible just below near the front of the engines. It is in Desert colours.
The book, Osprey Blenheim Squadrons of WW2 mentions that - "many Desert Air Force Blenheim squadrons fitted 20mm cannon for ground strafing. Without such a weapon, the Blenheim had to approach its targets too closely, bringin it within easy reach of enemy small arms." (page 84).
The same book has what I think may be a more accurate profile of the plane that is depicted in your image. It is on page 41. Here it is.
Blenheim IVF Z/7513/B of Number 15 Squadron SAAF, Cyrenaica Libya April 1942.
There is no perfectly accurate book/source. Here is an example to illustrate. The following image is from the Squdron Signal Blenheim in action book.
And here is the same image in another book. Note that the image has been doctored to make it look as though there is a nose mounted gun.
So stay skeptical.