In order to convert JPEG picture (.jpg, .jpeg) to a 3D model for printing, you would have to use a program capable of generating 3D meshes from pictures. You can find plenty of tutorials all over internet for this procedure, even some informative "how to" YouTube videos do nicely explain how to convert pictures for 3D printing.
Convert JPEG bitmap image format to Stereolithography CAD file.
We have found 2 software records in our database eligible for .jpg to .stl file format conversion.
Microsoft Windows software - convert jpg to stl on Windows
A 3D CAD translation softwate
Convert from jpg file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned jpg to stl. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A 3D general-purpose modeling program