The IP750 IDP add-in is an environment for developing an image processing library (IDP Add-in Library). It enables the creation of a customized image processing function without modifying IG-XL source code in the IDP add-in and the add-in functions can be executed in a multi-threaded environment without coding a multi-threaded unique process. The IDP Add-in Library has some API functions that Teradyne has provided for add-in development but users could also develop their own functions to either implement more common image data processing or adopt special algorithms for image data analysis in the IDP Add-in Library. However, if there is a need to maintain confidentiality of a custom algorithm a specific implementation of the algorithm will be required by calling a custom DLL in the IDP Add-in Library. This presentation will describe how to develop a customized DLL that could be invoked in the IP750 IDP Add-in Library and how to debug it in Microsoft Visual Studio IDE when IG-XL is running.