If you are automating the app registration using Selenium IDE that contains captchas, record and replay would not work because the captchas would change every time new user registers into the application.
This can be achieved by using storeEval command. The execution of the automation script stops at that point, waits for the manual entry of code and it resumes execution of subsequent commands.
Source code:
<tr>
<td>storeEval</td>
<td>prompt("Please enter captcha");</td>
<td>captcha</td>
</tr>
<tr>
<td>type</td>
<td>//*[@id='hip']</td>
<td>${captcha}</td>
</tr>