Vector programs are drawing programs so converting a photograph into vector format means making a drawing of the photo.

Photo vs drawing. Vector vs Raster

Electronic images are usually either a photograph or an illustration (drawing) and they can be either in raster format or vector format.

photo vs drawings raster vs vector

A vector drawing can be made of a photograph that is so detailed it can resemble the photograph almost identically. This would require a multitude of color objects, too many for the file to be useful for some of the services that require vector art such as specialty signs and printing. Or it would require the use of raster effects such as gradients and shadows in which case the file won't be suitable for those processes that require 100% true vector art.

Below is a photograph converted to vector format using automated tracing with a multitude of colors. This vector image is not suitable for many services including some specialty sings and printing.

photo vs drawings raster vs vector

Below is a photograph drawn in vector format. Left: original photograph. Middle: simple vector illustration suitable for all processes. Far right: The use of gradients makes this image unsuitable for processes that require 100% vector art.

raster photo vs vector drawing with raster effects