Can't add image to screen group within a local function [LUA, CORONA SDK STORYBOARD]

Question

When I use screenGroup:insert(img) I get "attempt to index global 'screenGroup' (a nil value)".
How do I add the img objects created in the onTouch function to the screenGroup to ensure they are removed when I change scenes?

local storyboard = require( "storyboard" )
local scene = storyboard.newScene()

local function goToTitle(event)
    if event.phase == "began" then
        storyboard.gotoScene( "titleScreen",  "fade", 400  )
    end
    return true
end

local onTouch = function(event)
    if event.phase == "began" then
        local img = display.newImage("shut_up_black.jpg")
        img:addEventListener( "touch", goToTitle ) 
        img.width = 100
        img.height = 100
        img.x = event.x
        img.y = event.y
        screenGroup:insert(img)
        return true
    end
end

function scene:createScene( event )
    local screenGroup = self.view
    local bg = display.newImage("bg1.jpg")
    screenGroup:insert( bg )
    Runtime:addEventListener("touch", onTouch)
end

function scene:enterScene( event )
end

function scene:exitScene( event )
end

function scene:destroyScene( event )
end

scene:addEventListener( "createScene", scene )
scene:addEventListener( "enterScene", scene )
scene:addEventListener( "exitScene", scene )
scene:addEventListener( "destroyScene", scene )

return scene

Answer 1

You declared sceneGroup as local in createScene so it does not exist outside of that function. Move the declaration to the top of the file:

local screenGroup

Then in createScene just do

screenGroup = self.view

You can specify the group in which to put image as first parameter to newImage although the way you insert it is fine too.