AFAIK, image files are stored unmodified into the .lfm files (if you load an image in a TImage.Picture property at design time in the IDE for instance - so, also stored unmodified into the resource data of your final executable file).
So, the answer to your question is : yes, you have to remove sensible data first, prior to incorporate your image files into your project data (i.e. into your picture in the Lazarus IDE at design time, for instance; or also "directly", as external resources).