**Steps to reproduce:**
1. PHP 8.1.8 without GD installed
2. Create a project
3. Go to http://phorge.localhost/project/manage/1/
4. Select {nav icon=picture, name=Edit Picture} in the sidebar on the right to go to
the `Edit Project Picture` at http://phorge.localhost/project/picture/1/
5. On `Custom: Choose Icon and Color...`, `Choose Background Color` and `Choose Icon`, then click the `Save Image` button.
**Actual outcome:**
```
[2023-05-01 22:25:09] EXCEPTION: (Error) Call to undefined function imagecreatefromstring() at [<phorge>/src/applications/files/builtin/PhabricatorFilesComposeIconBuiltinFile.php:131]
arcanist(head=T15263, ref.master=82d1abd4edd1, ref.T15263=4324d11c8b49), phorge(head=master, ref.master=8f669ea08289)
#0 phlog(Error) called at [<phorge>/src/aphront/handler/PhabricatorDefaultRequestExceptionHandler.php:41]
#1 PhabricatorDefaultRequestExceptionHandler::handleRequestThrowable(AphrontRequest, Error) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:751]
#2 AphrontApplicationConfiguration::handleThrowable(Error) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:296]
#3 AphrontApplicationConfiguration::processRequest(AphrontRequest, PhutilDeferredLog, AphrontPHPHTTPSink, MultimeterControl) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:204]
#4 AphrontApplicationConfiguration::runHTTPRequest(AphrontPHPHTTPSink) called at [<phorge>/webroot/index.php:35]
```
**Expected outcome:**
Either a friendlier error message explaining what to do.
Or no error message at all.
**Other comments:**
Since PHP 8.0.0, PHP's `imagecreatefromstring()` ["returns a GDImage instance on success; previously, a resource was returned."](https://www.php.net/manual/en/function.imagecreatefromstring.php)
Thus there is a currently undocumented requirement to have the PHP GD extension installed: https://www.php.net/manual/en/image.installation.php
I can confirm that installing `php-gd-8.1.18` fixes the problem.