一般看来文字与图片是毫不相同的，但是它们却有共同点。图片是由一个个点组成的，而这些点的颜色值可由数字组成，文字可由ASCII码表示，这就使得数字成为它们之间沟通道桥梁。因此就可以将文本藏入图片中。
这可以用Visual Basic 6.0实现，首先我们将文字转化为数字，再将图片中的每个点的RGB值取出，将数字每三个分别与Ｒ值，G值，B值相加或相减，接着把RGB值还原为图片中的点，至此我们已经将文本藏入图片。要取出文本怎么办呢？我们可以把源图片与目标图片进行对比，将到的差值转化为文本，就实现了文本的还原。
具体作法：先建立窗体文件frmPictureText.frm和模块文件modPictureText.bas
模块文件：
Public Declare Function GetObject Lib "gdi32" Alias "GetObjectA" (ByVal _
hObject As Long, ByVal nCount As Long, lpObject As Any) As Long
'用于获得图片的象素
Public Declare Function GetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x _
As Long, ByVal y As Long) As Long '用于获得图片指定点的RGB值
Public Type BITMAP
bmType As Long
bmWidth As Long
bmHeight As Long
bmWidthBytes As Long
bmPlanes As Integer
bmBitsPixel As Integer
bmBits As Long
End Type
Function HexDec(Number As String) As Integer '将十六进制转化为十进制
Dim n As Integer, dec As String, tmp As Integer
For n = 1 To Len(Number)
dec = Mid(Number, n, 1)
If Asc(dec) >= 65 Then
dec = UCase(dec)
dec = Format(Asc(dec) - 55)
End If
tmp = Val(dec) * 16 ^ (Len(Number) - n)
HexDec = HexDec + tmp
Next n
End Function
窗体文件：建立两个图片框:picSource用于显示源图片，picObject用于显示目标图片，
建立两个文本框：txtSource用于显示源文本，txtObject用于显示还原的文本，并设置为各多行显示，建立两个命令按钮：cmdTextToPicture用于把文本藏入图片，cmdPictureToText用于还原文本。
Private Sub Form_Load()
picSource.AutoRedraw = True: picObject.AutoRedraw = True
picSource.AutoSize = True: picObject.AutoSize = True
picSource.Picture = LoadPicture("c:/test.bmp")
picObject.Height = picSource.Height '设置目标图片框的Height和
picObject.Width = picSource.Width 'Width属性与源图片相同,保证
'目标图片的大小和源文件相同
End Sub
Private Sub cmdTextToPicture_Click()
Dim numX As Integer, chrTmp As String, numTmp As Integer, numY As Integer, word As String
Dim souPixel As BITMAP, souTop As Integer, souLeft As Integer
Dim souColor As Long, souGetcolor As String, numN As Integer
Dim tmpWord As String, numDifRed As Integer, numDifGreen As Integer, numDifBlue As Integer
Dim newRed As Integer, newGreen As Integer, newBlue As Integer
On Error Resume Next
Kill "c:/temp1.txt"
Open "c:/temp1.txt" For Append As #1 '将文本转化为数字,并存入文件
For numX = 1 To Len(txtSource.Text)
numTmp = Asc(Mid(txtSource.Text, numX, 1))
chrTmp = Format(numTmp)
If numTmp >= 0 Then chrTmp = "+" & chrTmp
For numY = 1 To Len(chrTmp)
word = Format(Asc(Mid(chrTmp, numY, 1)))
Print #1, word;
Next numY
Next numX
Close #1
Open "c:/temp1.txt" For Input As #2
GetObject picSource.Picture.Handle, Len(souPixel), souPixel
picObject.Picture = Nothing: picObject.Cls
For souTop = 0 To souPixel.bmHeight - 1
For souLeft = 0 To souPixel.bmWidth - 1
'取出图片各点的RGB值
souColor = GetPixel(picSource.hdc, souLeft, souTop)
souGetcolor = Hex(souColor)
numN = 6 - Len(souGetcolor)
souGetcolor = String(numN, "0") & souGetcolor
'取出三个数字
If Not (EOF(2)) Then
tmpWord = Input(3, #2)
numDifRed = Val(Left(tmpWord, 1))
numDifGreen = Val(Mid(tmpWord, 2, 1))
numDifBlue = Val(Right(tmpWord, 1))
End If
'把数字与R值,G值,B值相加或相减
newRed = HexDec(Right(souGetcolor, 2)) - numDifRed
If newRed < 0 Then newRed = HexDec(Right(getcolor, 2)) + numDifRed
newGreen = HexDec(Mid(souGetcolor, 3, 2)) - numDifGreen
If newGreen < 0 Then newGreen = HexDec(Mid(souGetcolor, 3, 2)) + numDifGreen
newBlue = HexDec(Left(souGetcolor, 2)) - numDifBlue
If newBlue < 0 Then newBlue = HexDec(Left(souGetcolor, 2)) + numDifBlue
numDifRed = 0: numDifGreen = 0: numDifBlue = 0
DoEvents
'形成目标图片
picObject.PSet (souLeft, souTop), RGB(newRed, newGreen, newBlue)
Next souLeft
Next souTop
Close #2
SavePicture picObject.Image, "c:/object.bmp"
picObject.Picture = LoadPicture("c:/object.bmp")
End Sub
Private Sub cmdPictureToText_Click()
Dim Pixel As BITMAP
Dim souTop As Integer, souLeft As Integer
Dim souColor As Long, objColor As Long, souGetcolor As String, objGetcolor As String
Dim souRed As Integer, souGreen As Integer, souBlue As Integer
Dim objRed As Integer, objGreen As Integer, objBlue As Integer
Dim souN As Integer, objN As Integer
Dim numDifRed As Integer, chrDifRed As String
Dim numDifGreen As Integer, chrDifGreen As String
Dim numDifBlue As Integer, chrDifBlue As String
Dim Difference As String, numTmp As Integer, chrTmp As String, tmpWord As String, word As String
On Error Resume Next
GetObject picSource.Picture.Handle, Len(Pixel), Pixel '获取图片的象素
Kill "c:/temp2.txt" '如果存在"temp2.txt"文件,则将它清除
Open "c:/temp2.txt" For Append As #3
For souTop = 0 To Pixel.bmHeight - 1
For souLeft = 0 To Pixel.bmWidth - 1
'获得源图片各点的RGB值
souColor = GetPixel(picSource.hdc, souLeft, souTop)
souGetcolor = Hex(souColor)
souN = 6 - Len(souGetcolor)
souGetcolor = String(souN, "0") & souGetcolor
souRed = HexDec(Right(souGetcolor, 2)) '转化为Red,Green,Blue的值
souGreen = HexDec(Mid(souGetcolor, 3, 2))
souBlue = HexDec(Left(souGetcolor, 2))
'获得目标图片各点的RGB值
objColor = GetPixel(picObject.hdc, souLeft, souTop)
objGetcolor = Hex(objColor)
objN = 6 - Len(objGetcolor)
objGetcolor = String(objN, "0") & objGetcolor
objRed = HexDec(Right(objGetcolor, 2))
objGreen = HexDec(Mid(objGetcolor, 3, 2))
objBlue = HexDec(Left(objGetcolor, 2))
numDifRed = souRed - objRed '将差值存入文件
chrDifRed = Format(numDifRed)
If numDifRed < 0 Then chrDifRed = Format(objRed - souRed)
numDifGreen = souGreen - objGreen
chrDifGreen = Format(numDifGreen)
If numDifGreen < 0 Then chrDifGreen = Format(objGreen - souGreen)
numDifBlue = souBlue - objBlue
chrDifBlue = Format(numDifBlue)
If numDifBlue < 0 Then chrDifBlue = Format(objBlue - souBlue)
Difference = chrDifRed & chrDifGreen & chrDifBlue
Print #3, Difference;
Next souLeft
Next souTop
Close #3
Open "c:/temp2.txt" For Input As #4 '从文件还原文字
Do While Not EOF(4)
numTmp = Input(2, #4)
chrTmp = Chr(Val(numTmp))
If (Len(tmpWord) > 1) And (chrTmp = "+" Or chrTmp = "-") Then
word = Chr(Val(tmpWord))
txtobject.Text = txtobject.Text & word
tmpWord = ""
End If
tmpWord = tmpWord & chrTmp
Loop
txtobject.Text = txtobject.Text & Chr(Val(tmpWord))
Close #4
End Sub
以上程序在Windows98系统中VB6.0中调试通过。
综上所述，此方法对图片各点的RGB值的修改范围为0～9，很难区别目标图片与源图片，因此可以用于文件的加密。
