Image does not load - purple and black squares instead of a picture

My config mainmenu.json:

`{
"images":
{
"title":
{
"image" : "resources/mainmenu/asdf.png",
"posX" : -137,
"posY" : 30,
"width" : 512,
"height" : 512,
"alignment" : "top_center"
}
},

"buttons":
{
    "singleplayer":
    {
        "text" : "menu.singleplayer",
        "posX" : -100,
        "posY" : 48,
        "width" : 200,
        "height" : 20
    },
    
    "multiplayer":
    {
        "text" : "menu.multiplayer",
        "posX" : -100,
        "posY" : 72,
        "width" : 200,
        "height" : 20
    },
    
    "mods":
    {
        "text" : "fml.menu.mods",
        "posX" : -100,
        "posY" : 96,
        "width" : 200,
        "height" : 20
    },
        
    "options":
    {
        "text" : "menu.options",
        "posX" : -100,
        "posY" : 132,
        "width" : 98,
        "height" : 20
    },
    
    "quit":
    {
        "text" : "menu.quit",
        "posX" : 2,
        "posY" : 132,
        "width" : 98,
        "height" : 20
    },
    
    "language":
    {
        "text" : "",
        "posX" : -124,
        "posY" : 132,
        "width" : 20,
        "height" : 20
    },
    
    "refresh":
    {
        "text" : "",
        "posX" : -154,
        "posY" : 132,
        "width" : 20,
        "height" : 20
    }
},

"texts":
{
    "mojang":
    {
        "text" : "",
        "posX" : -197,
        "posY" : -10,
        "color" : -1,
        "alignment" : "bottom_right"
    },
    
    "fml":
    {
        "text" : "",
        "posX" : 2,
        "posY" : -50,
        "color" : -1,
        "alignment" : "bottom_left"
    }
},

"other":
{
    "splash-text":
    {
        "posX" : 90,
        "posY" : 70,
        "color" : -256,
        "alignment" : "top_center"
    },
    
    "background":
    {
        "image" : "resources/mainmenu/asdf.png",
        "mode" : "fill"
    }
}

}`

There is a 3840x2160 image stored in the file .minecraft\resources\mainmenu\asdf.png

I tried to use all sorts of path recording options - it doesn't work.