BMP (Windows Bitmap) is a raster-based format that uses colored dots to represent an image. BMP format can't be compressed and the file size tends to be larger than other raster-based formats (.png, .jpg, .gif, .tif, and others).
EMF (Enhanced Metafile) is a 32-bit vector-based format that stores information as mathematically-based vectors. EMF images can be scaled and the file format is compressed. EMF format is extensible so that custom functionality can be embedded in the emf file.