How can you tell if an exe depends on qgif4.dll, qjpeg4.dll, qtiff4.dll?
They all implement these functions:
dumpbin probably isnt smart enough to see if any of qgif4.dll, qjpeg4.dll, qtiff4.dll could be called indirectly by an executable.
Of course we need to supply all dlls needed by our app. But we want to only supply what is essential, since the app has to run on a stripped down embedded version of Windows XP with size constraints: all is run from virtal RAM disk.
Since those are plugins and loaded during runtime on as-needed-basis.
To add to @raven-worx, in your case you should exactly now what kind plugins your application need.
Depending on the restriction you face, you might also want to consider building a stripped down version of Qt with only the functions your need.