SteamAvatar.cs

using UnityEngine;
using Facepunch.Steamworks;
using UnityEngine.UI;

//
// To change at runtime set SteamId then call Fetch()
//
public class SteamAvatar : MonoBehaviour
{
    public ulong SteamId;
    public Friends.AvatarSize Size;
    public Texture FallbackTexture;

    void Start()
    {
        Fetch();
    }

    public void Fetch()
    {
        if (SteamId == 0) return;
        if (Client.Instance == null)
        {
            ApplyTexture(FallbackTexture);
            return;
        }

        Client.Instance.Friends.GetAvatar(Size, SteamId, OnImage);
    }

    private void OnImage( Facepunch.Steamworks.Image image )
    {
        if ( image == null )
        {
            ApplyTexture(FallbackTexture);
            return;
        }

        var texture = new Texture2D(image.Width, image.Height);

        for (int x = 0; x < image.Width; x++)
            for (int y = 0; y < image.Height; y++)
            {
                var p = image.GetPixel(x, y);

                texture.SetPixel(x, image.Height - y, new UnityEngine.Color( p.r / 255.0f, p.g / 255.0f, p.b / 255.0f, p.a / 255.0f ) );
            }

        texture.Apply();

        ApplyTexture(texture);
    }

    private void ApplyTexture(Texture texture)
    {
        var rawImage = GetComponent<RawImage>();
        if (rawImage != null)
            rawImage.texture = texture;
    }
}