| Type | Example | Source | Features |
| Solid CAPTCHA | | Discuz! | Character independent, texture background, some interference | | Slashdot | A large number of interference lines and noise points | | Gimpy | Multiple strings, overlap, distortion | | Google | Unfixed length, distortion, adhesion | | Microsoft | Double-string, unfixed length, uneven thickness, tilting, adhesion |
| Hollow CAPTCHA | | QQ | Hollow, shadows, interference shapes | | Sina | Hollow, adhesion, interference lines | | Yandex | Hollow, virtual contours, distortion, adhesion, interference lines |
| Three-dimensional CAPTCHA | | Scihub | Hollow, shadows, interference lines, noise points | | Teabag | Grids, protrusion, distortion, background and character blending | | Parc | Colorful, shadow, rotation, zoom | Special characters |
| Animation CAPTCHA | | Program generating | Multiple characters jumping | | Hcaptcha | Multilayer character images blinking transformation |
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