The front end user cannot user JCE editor right now, so how can front user upload the images like backend user does.

Hi. What do you mean that the user cannot use JCE? Is the editor loaded in K2 front-end editing or not?

hey, make sure that access level is set to where whom you want to use the editor can use it. Also, there are permissions set with JCE that varies what can and can't be accessed on the front end- look all that over
normal front end use for editor would require a mangaer author status access level. You don't want any idiot going into the editor