I assume you have some knowledge of Visual Basic.NET so I won't spoon feed you guys today.

Create a new windows form project and add the following controls:

• [*] One TextBox
  [*] One PictureBox
  [*] One Button
  

This is mine:


Step 1
First, let us make the Function which generates the random string.

Code:

Private Shared Function RandomString(ByVal size As Integer) As String
            Dim random As New Random() ' Define a new random class, we can't do this inside the code, since it will then return only one letter.
            RandomString = Nothing ' Set the string to Empty/Nothing
            For i = 0 To size - 1 ' From 0 to size - 1
                RandomString += Convert.ToChar(Convert.ToInt32((25 * random.NextDouble() + 65))) ' Generate, convert and add.
            Next
            Return RandomString ' Return the string.
        End Function

I fully commented everything so you know what piece of code does what.

Step 2
Okay, cool, we get l33t strings. But how we get them into a image?

Simple:

Code:

Public Shared Sub RandomImage(ByVal p As PictureBox, ByVal c As Color, Optional ByVal string_size As Integer = 6, Optional ByVal letter_size As Integer = 30)
            p.Refresh() ' Remove (if ít's there) the old captcha.
            Dim g As Graphics = p.CreateGraphics ' Assign our Graphics class to the picturebox.
            s = RandomString(string_size) 'Save and generate the new captcha
            g.DrawString(s, New Font(Form1.Font.OriginalFontName, letter_size, FontStyle.Regular), New SolidBrush(c), 0, 0, New StringFormat) ' Draw the string using Graphics.
        End Sub

As you notice, I'm trying to declare as less as I can.

Step 3
Now we are going to check if the picture matches the textbox.

First we need to store the string into the memory, (as you notice a error) so we need to declare 's'.

Code:

Private Shared s As String = Nothing ' Save it to check it later.

Next, the actual check:

Code:

Public Shared Function Check(ByVal str As String) As Boolean
            If str.ToUpper() = s Then Return True Else Return False ' If the stored string matches the parameter(textbox) its string, return true, else return false.
            ' String is generated in Uppercase, so convert the parameter(textbox) to uppercase.
        End Function

Step 4

Double click the button, we need to call the 'Check' function and insert the textbox its text into the parameter.

Code:

If ManCaptcha.Check(TextBox1.Text) Then ' Check if true.
            MsgBox("Passed!") ' Show a confirmation.
            ' Parameters: <picturebox to store picture>, <color of captcha>, <size of captcha string>, <size of each letter>  
            ManCaptcha.RandomImage(PictureBox1, Color.Red, 6, 30) ' Create a new one.
            TextBox1.Clear() ' Clear the textbox.
        Else
            MsgBox("Retry!") ' Show a error.
        End If

NOTE: I placed everything from Step 1 to Step 3 in a STRUCTURE

Code:

Structure ManCaptcha
End Structure

You can skip it, but I like to have it organized.

Step 5

Now, to create the image and draw it, you can use this:

Please comment & rate!

(06-09-2011, 07:49 AM)xMan Wrote: wow this is one in depth tutorial. well done with it!

(06-09-2011, 07:48 AM)davidmarker Wrote: Thanks! I'll have to implant this in some of my future projects.

(06-14-2011, 02:21 AM)-Dreams Wrote: Kinda dumb in my book, but whatever.