There are 2 types of files we work with.
One is is bitmaps or raster, which is like your tv or monitor. The image is made of pixels. Photos are rasters.
The other file type is vector. The image is made up of vectors or lines. This is what you need to cut on your plotter.
You can usually tell what the image will be like by the file type. .tif .jpg will always be raster. .plt .dxf will always be vector. Some like .eps and .pdf can be either vector or raster or both. So saving a .jpg to .eps does nothing to alter the file contents other than changing the name.
As others have stated you must trace the raster or photo image to get the vectors.