You're using the CameraCaptureTask class (or a library you are referencing is using this class) in your Windows Phone app. When you run the Marketplace Test kit, the ID_CAP_CAMERA capability is not detected.
When you submit your application to the Marketplace, the Marketplace does detect the camera capability. And the marketplace page for your application will say your app uses the Camera. This can come as a surprise, because the Marketplace Test Kit did not detect it.
Luckily, there's a way to fix this.
Add your own rules to the Marketplace Test Kit
Open the Rules.xml file:
%ProgramFiles%\Microsoft SDKs\Windows Phone\v7.1\Tools\Marketplace\Rules.xml
These are the rules the Marketplace Test kit uses for detecting capabilities.
Find the ID_CAP_CAMERA capability.
Add these lines:
<Assembly Name="Microsoft.Phone, Version=188.8.131.52, Culture=neutral, PublicKeyToken=24eec0d8c86cda1e">
<Class Name="CameraCaptureTask" />
Save the file and run the Marketplace Test kit again. Now it works as expected!