Creates GL texture from image in stream in format supported by Imaging.

function LoadGLTextureFromStream(Stream: TStream; 
                                 CreatedWidth: PLongInt = nil; 
                                 CreatedHeight: PLongInt = nil): GLuint;

ImagingOpenGL (at line 97)

You can use CreatedWidth and Height parameters to query dimensions of created textures (it could differ from dimensions of source image).