Member Avatar for cocoll

hello!
if we sign up at a hotmail account or other account we see before submit our information that we must enter a words and that is for prevent "robots" to sign up with hundreds of accounts.
so this characters is an image,so what i want is your help in this:
i want to create this image so what i know is this:
i can generate random characters it's not so difficult and i can build a string from them ,then i can create an image with that string but i can give the string the format that we can see at sign up at any account so i tried to play with "font-family" with no success so i need your help in this and if you can tell me the difference in asp.net=create this image,because i used vb.net with a pictureBox.
thank you very much.

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  • Latest Post Latest Post by dnanetwork

Dani AI

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Short summary for (and following ’s suggestion): a CAPTCHA string is drawn on the server and sent as an image — CSS font-family won’t change what’s already been rasterized into a bitmap. The usual pattern is: generate a random string server‑side, store the correct value on the server (Session, cache, DB) with a short TTL, and expose an image endpoint (Generic Handler / controller action) that returns the rendered bytes with the right ContentType (for example image/png). (sitepoint.com)

A compact VB.NET ASHX example showing the core idea (create bitmap, draw warped text, stream to response):

<%@ WebHandler Language="VB" Class="CaptchaHandler" %>

Imports System.Web
Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Drawing.Imaging
Imports System.Web.SessionState

Public Class CaptchaHandler : Implements IHttpHandler, IRequiresSessionState

  Public Sub ProcessRequest(ctx As HttpContext) Implements IHttpHandler.ProcessRequest
    Dim rnd As New Random()
    Dim text = rnd.Next(1000, 9999).ToString()
    ctx.Session("captcha") = text

    Using bmp As New Bitmap(200, 60)
      Using g = Graphics.FromImage(bmp)
        g.SmoothingMode = SmoothingMode.AntiAlias
        g.Clear(Color.White)
        Dim f As New Font("Arial", 28, FontStyle.Bold)
        Dim path As New GraphicsPath()
        path.AddString(text, f.FontFamily, CInt(f.Style), f.Size, New RectangleF(0,0,200,60), StringFormat.GenericDefault)
        path.Warp(New PointF() {New PointF(0,0), New PointF(200,5), New PointF(0,60)}, New RectangleF(0,0,200,60), Nothing, WarpMode.Perspective, 0.5F)
        g.FillPath(Brushes.Black, path)
        ' add lines/dots/noise here before output
      End Using
      ctx.Response.ContentType = "image/png"
      bmp.Save(ctx.Response.OutputStream, ImageFormat.Png)
    End Using
  End Sub

  Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
    Get
      Return False
    End Get
  End Property
End Class

Use GraphicsPath.AddString + GraphicsPath.Warp (or small random rotations, jittered glyph positions, arcs, and line/noise overlays) to get the “distorted” look; see the GraphicsPath/Warp API for details. (learn.microsoft.com)

Notes and cautions: System.Drawing (System.Drawing.Common) works fine on Windows hosts but is not supported on non‑Windows in modern .NET without workarounds — for cross‑platform or cloud hosts prefer a maintained library such as SixLabors.ImageSharp (or SkiaSharp) which has safer server usage patterns. (learn.microsoft.com)

Security: homemade CAPTCHAs can be broken by modern OCR/ML. For production consider a managed service (reCAPTCHA, hCaptcha, etc.) or combine your image CAPTCHA with rate limits, per‑session tokens, short expiry, and secondary checks. ’s pointer to ReCaptcha is sensible for production systems. (developers.google.com)

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Member Avatar for cocoll

thank you for your reply.
first the 2 links are useful,and re-captcha is what i need but not like an application because i don't have a website so i want to build something like that,so just i need to know how can i give that form to the string image.
thank you very much.

Member Avatar for dnanetwork

if problem is resolved then mark your thread as resolved.

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