diff --git a/README.md b/README.md
index 2eb4ebe..f5ab709 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 CaptchaKit is an ASP.NET Core CAPTCHA foundation with server-side, one-time validation and pluggable generators and storage.
 
-`CaptchaKit.Core` has provider-neutral contracts. `CaptchaKit.AspNetCore` supplies randomized text-image, selection, and one-click challenges with `IDistributedCache` storage.
+`CaptchaKit.Core` has provider-neutral contracts. `CaptchaKit.AspNetCore` supplies randomized distorted-text, image-math, and image-target-selection challenges with `IDistributedCache` storage.
 
 The package does not claim that image CAPTCHA alone defeats determined automation. Deploy it with rate limits, account lockout, and appropriate risk controls.
 
diff --git a/src/CaptchaKit.AspNetCore/CaptchaKit.AspNetCore.csproj b/src/CaptchaKit.AspNetCore/CaptchaKit.AspNetCore.csproj
index 04dac06..22b6c13 100644
--- a/src/CaptchaKit.AspNetCore/CaptchaKit.AspNetCore.csproj
+++ b/src/CaptchaKit.AspNetCore/CaptchaKit.AspNetCore.csproj
@@ -5,7 +5,7 @@
     <Nullable>enable</Nullable>
     <GeneratePackageOnBuild>false</GeneratePackageOnBuild>
     <PackageId>CaptchaKit.AspNetCore</PackageId>
-    <Version>0.1.0-preview.2</Version>
+    <Version>0.1.0-preview.3</Version>
     <Authors>CaptchaKit Contributors</Authors>
     <Description>ASP.NET Core and distributed-cache integration for CaptchaKit.</Description>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
diff --git a/src/CaptchaKit.AspNetCore/CaptchaKitService.cs b/src/CaptchaKit.AspNetCore/CaptchaKitService.cs
index 8451ebd..dead738 100644
--- a/src/CaptchaKit.AspNetCore/CaptchaKitService.cs
+++ b/src/CaptchaKit.AspNetCore/CaptchaKitService.cs
@@ -13,7 +13,7 @@ public sealed class CaptchaKitOptions
     public TimeSpan Lifetime { get; set; } = TimeSpan.FromMinutes(2);
     public string CacheKeyPrefix { get; set; } = "captchakit:";
     public bool RequireBrowserProof { get; set; }
-    public bool EnableOneClickChallenge { get; set; } = true;
+    public bool EnableMathChallenge { get; set; } = true;
     public bool EnableSelectionChallenge { get; set; } = true;
 }
 
@@ -85,33 +85,41 @@ public sealed class DistributedCaptchaChallengeStore(
 public sealed class RandomCaptchaGenerator(CaptchaKitOptions options) : ICaptchaGenerator
 {
     private readonly SkiaTextCaptchaGenerator _text = new();
+    private const string SelectionAlphabet = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789";
 
     public GeneratedCaptcha Generate(CaptchaGenerationRequest request)
     {
         var roll = RandomNumberGenerator.GetInt32(100);
-        if (options.EnableOneClickChallenge && roll < 15)
+        if (options.EnableMathChallenge && roll < 25)
         {
-            return new GeneratedCaptcha(
-                new CaptchaChallenge(request.Id, CaptchaChallengeType.OneClick, request.ExpiresAt,
-                    "请点击确认按钮继续登录"),
-                "CONFIRM");
+            var left = RandomNumberGenerator.GetInt32(2, 10);
+            var right = RandomNumberGenerator.GetInt32(1, 10);
+            var isAddition = RandomNumberGenerator.GetInt32(2) == 0;
+            if (!isAddition && right > left)
+                (left, right) = (right, left);
+            var expression = $"{left} {(isAddition ? '+' : '-')} {right} = ?";
+            var answer = (isAddition ? left + right : left - right).ToString();
+            return _text.CreateVisualChallenge(
+                request, expression, answer, CaptchaChallengeType.MathImage, "请计算图片中的算式");
         }
-        if (options.EnableSelectionChallenge && roll < 45)
+        if (options.EnableSelectionChallenge && roll < 55)
         {
-            var correct = RandomNumberGenerator.GetInt32(2, 10).ToString();
-            var candidates = Enumerable.Range(1, 9)
-                .Where(x => x.ToString() != correct)
+            var target = SelectionAlphabet[RandomNumberGenerator.GetInt32(SelectionAlphabet.Length)].ToString();
+            var candidates = SelectionAlphabet
+                .Select(x => x.ToString())
+                .Where(x => x != target)
                 .OrderBy(_ => RandomNumberGenerator.GetInt32(int.MaxValue))
                 .Take(3)
-                .Append(int.Parse(correct))
+                .Append(target)
                 .OrderBy(_ => RandomNumberGenerator.GetInt32(int.MaxValue))
-                .Select(x => new CaptchaChoice($"choice-{x}", x.ToString()))
+                .Select(x => new CaptchaChoice($"choice-{x}", x))
                 .ToList();
-            var answer = candidates.Single(x => x.Label == correct).Id;
+            var answer = candidates.Single(x => x.Label == target).Id;
+            var visual = _text.CreateVisualChallenge(
+                request, target, answer, CaptchaChallengeType.Selection, "请选择与图片中字符相同的一项");
             return new GeneratedCaptcha(
-                new CaptchaChallenge(request.Id, CaptchaChallengeType.Selection, request.ExpiresAt,
-                    $"请选择数字 {correct}", candidates),
-                answer);
+                visual.Challenge with { Choices = candidates },
+                visual.Answer);
         }
         return _text.Generate(request);
     }
@@ -125,27 +133,39 @@ public sealed class SkiaTextCaptchaGenerator : ICaptchaGenerator
     {
         var answer = string.Concat(Enumerable.Range(0, request.CodeLength)
             .Select(_ => Alphabet[RandomNumberGenerator.GetInt32(Alphabet.Length)]));
-        using var bitmap = new SKBitmap(160, 54);
+        return CreateVisualChallenge(request, answer, answer, CaptchaChallengeType.TextImage, "请输入图中的字符");
+    }
+
+    public GeneratedCaptcha CreateVisualChallenge(
+        CaptchaGenerationRequest request,
+        string displayText,
+        string answer,
+        CaptchaChallengeType type,
+        string prompt)
+    {
+        var width = Math.Max(160, 20 + displayText.Length * 27);
+        using var bitmap = new SKBitmap(width, 54);
         using var canvas = new SKCanvas(bitmap);
         canvas.Clear(new SKColor(244, 248, 252));
-        DrawNoise(canvas, 160, 54, 13);
+        DrawNoise(canvas, width, 54, 16);
         using var paint = new SKPaint { IsAntialias = true };
         using var font = new SKFont(SKTypeface.FromFamilyName("Arial", SKFontStyle.Bold), 30);
-        for (var index = 0; index < answer.Length; index++)
+        var spacing = Math.Max(22, (width - 24) / displayText.Length);
+        for (var index = 0; index < displayText.Length; index++)
         {
-            var x = 14 + index * 29 + RandomNumberGenerator.GetInt32(-2, 3);
+            var x = 12 + index * spacing + RandomNumberGenerator.GetInt32(-2, 3);
             var y = 38 + RandomNumberGenerator.GetInt32(-4, 5);
             paint.Color = RandomColor(35, 145);
             canvas.Save();
             canvas.RotateDegrees(RandomNumberGenerator.GetInt32(-20, 21), x, y);
-            canvas.DrawText(answer[index].ToString(), x, y, SKTextAlign.Left, font, paint);
+            canvas.DrawText(displayText[index].ToString(), x, y, SKTextAlign.Left, font, paint);
             canvas.Restore();
         }
-        DrawNoise(canvas, 160, 54, 8);
+        DrawNoise(canvas, width, 54, 10);
         using var image = SKImage.FromBitmap(bitmap);
         using var data = image.Encode(SKEncodedImageFormat.Png, 100);
-        var challenge = new CaptchaChallenge(request.Id, CaptchaChallengeType.TextImage, request.ExpiresAt,
-            "请输入图中的字符", null, "image/png", data.ToArray());
+        var challenge = new CaptchaChallenge(request.Id, type, request.ExpiresAt,
+            prompt, null, "image/png", data.ToArray());
         return new GeneratedCaptcha(challenge, answer);
     }
 
diff --git a/src/CaptchaKit.Core/CaptchaContracts.cs b/src/CaptchaKit.Core/CaptchaContracts.cs
index f63f342..af02c6f 100644
--- a/src/CaptchaKit.Core/CaptchaContracts.cs
+++ b/src/CaptchaKit.Core/CaptchaContracts.cs
@@ -3,6 +3,7 @@ namespace CaptchaKit;
 public enum CaptchaChallengeType
 {
     TextImage,
+    MathImage,
     Selection,
     OneClick
 }
diff --git a/src/CaptchaKit.Core/CaptchaKit.Core.csproj b/src/CaptchaKit.Core/CaptchaKit.Core.csproj
index 4d71f40..ab90cd1 100644
--- a/src/CaptchaKit.Core/CaptchaKit.Core.csproj
+++ b/src/CaptchaKit.Core/CaptchaKit.Core.csproj
@@ -5,7 +5,7 @@
     <Nullable>enable</Nullable>
     <GeneratePackageOnBuild>false</GeneratePackageOnBuild>
     <PackageId>CaptchaKit.Core</PackageId>
-    <Version>0.1.0-preview.2</Version>
+    <Version>0.1.0-preview.3</Version>
     <Authors>CaptchaKit Contributors</Authors>
     <Description>Provider-neutral, server-validated CAPTCHA challenge contracts.</Description>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>