How can I convert a .jpg image to an .eps?
ImageMagick can do this.
From the commandline, simply type:
convert filename.jpg filename.eps
(On Windows you may need to put in the full path to
convert.exe inside quotation marks; the above will work as-is on OS X or linux.)
It doesn't really make any sense to convert a raster graphic to a vector graphic, however. It'll still be rasterized.
Another way of doing it with a GUI would be to use Inkscape; I'm pretty sure it can import most formats, and it definitely can export to .eps — it does have some ways of trying to trace paths in a vector image to recreate the vectors, but it's far from failsafe.
Just be sure to "embed" rather than "link" when you import.
If you just want to convert an image or two to eps - use an online utility...
If you just want the jpeg image contained in the .eps file (and not vectorized), try this code
It's C++ source, and takes several image formats and puts them inside a compliant .eps file as an embedded image.
if the question involves postscript the answer is generally ghostscript / ghostview
I use online converter:
gimp is a great tool for converting files to other popular formats - http://www.gimp.org