It is possible to have transparent background on PNG and GIF image formats, but JPEG format doesn't support transparency. You can check image transparent background makers below. They are quite simple and easy to use. The last one allows to upload JPEG images, but output is in PNG format.
Transparent background making online tools:
PNG - Onlinepngtools.com
GIF - Onlinegiftools.com
JPEG - Onlinejpgtools.com