Invisible Ink Picture (Source Included)

BlitzMax Forums/BlitzMax Programming/Invisible Ink Picture (Source Included)

dw817

(Posted 2015) [#1]

Having received a Secret Invisible Ink pen I ordered from Ebay recently, I got to thinking about ALPHA transparency and came up with this interesting idea of hiding pictures online.

They appear invisible to everyone else, but if you save them, they can be revealed later. Here is the code to do it:

' Invisible Ink Picture by David W (dw817) 12-29-15
Strict
Global i,j,c,typ,pic:TPixmap,pic2:TPixmap,img:TImage,view$,hide$

Typ=1
' 0=Convert a picture to invisible ink and save it
' 1=Reveal a saved Invisible Ink picture

SetGraphicsDriver(GLMax2DDriver()) ' NECESSARY FOR AGGRESSIVE PIXEL READING & WRITING
Graphics 640,480

view$="spy-normal.png"
hide$="spy-hidden.png"

If typ
  pic=LoadPixmap(hide$)
  DrawPixmap pic,0,0
  Flip
  WaitKey
  End
EndIf

pic=LoadPixmap(view$)
pic2=CreatePixmap(128,128,pf_rgba8888)
For i=0 To 127
  For j=0 To 127
    c=ReadPixel(pic,j,i)-$ff000000
    WritePixel(pic2,j,i,c)
  Next
Next
img=LoadImage(pic2)
DrawImage img,0,0
If typ=0
  SavePixmapPNG pic2,hide$,9
EndIf
Flip
WaitKey
End

And here is your secret picture:

It's there ! Just click and save it as, "spy-hidden.png" and run the program.