1) Get the image xstring as below
cl_mime_repository_api=>get_api( )->get( EXPORTING i_url = 'IMAGE_URL' IMPORTING e_content = DATA(lv_xstring) ).
2) Use below code to encode xstring to base64 call function 'ssfc_base64_encode' exporting bindata = lv_xstring importing b64data = lv_img_str
3) Bind this field to an image field in the table
4) Make sure Embed Image Data is ticked