extracts icons from libraries. posted as answer to https://stackoverflow.com/questions/8435/how-do-you-get-the-icons-out-of-shell32-dll

Invoke-ExtractIconEx.ps1

Add-Type -AssemblyName System.Drawing

$refAssemblies = @(
    [Drawing.Icon].Assembly.Location

    if ($IsCoreCLR) {
        [psobject].Assembly.Location
        $pwshLocation = Split-Path -Path ([psobject].Assembly.Location) -Parent
        $pwshRefAssemblyPattern = [IO.Path]::Combine($pwshLocation, 'ref', '*.dll')
        (Get-Item -Path $pwshRefAssemblyPattern).FullName
    }
)

Add-Type @'
using System;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Drawing;
using System.IO;
using System.Management.Automation;
using System.Linq;

namespace ExtractIconEx
{
    [Cmdlet(VerbsLifecycle.Invoke, "ExtractIconEx")]
    [OutputType(typeof(FileInfo))]
    public sealed class InvokeExtractIconEx : PSCmdlet
    {
        [DllImport("shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        private static extern uint ExtractIconExW(
            [In] string lpszFile,
            [In] int nIconIndex,
            out IntPtr phiconLarge,
            out IntPtr phiconSmall,
            uint nIcons);

        [DllImport("shell32.dll", CharSet = CharSet.Unicode)]
        private static extern IntPtr ExtractIconW(
            [In] IntPtr hInst,
            [In] string lpszExeFileName,
            int nIconIndex);

        [DllImport("user32.dll")]
        private static extern bool DestroyIcon(IntPtr hIcon);

        [Parameter(Mandatory = true, Position = 0)]
        public string Source { get; set; }

        [Parameter(Position = 1)]
        [ValidateNotNullOrEmpty]
        public string Destination { get; set; }

        [Parameter(Position = 2)]
        public int[] Index { get; set; }

        protected override void EndProcessing()
        {
            Destination = string.IsNullOrWhiteSpace(Destination)
                ? SessionState.Path.CurrentFileSystemLocation.Path
                : GetUnresolvedProviderPathFromPSPath(Destination);

            if (Index == null)
            {
                Index = Enumerable
                    .Range(0, GetIconCount())
                    .ToArray();
            }

            foreach (int index in Index)
            {
                try
                {
                    WriteObject(
                        ExtractIcon(index),
                        enumerateCollection: true);
                }
                catch (Win32Exception exception)
                {
                    WriteError(new ErrorRecord(
                        exception, "IconExtractError", ErrorCategory.NotSpecified, null));
                }
            }
        }

        private int GetIconCount()
        {
            IntPtr nullPtr;
            uint result = ExtractIconExW(Source, -1, out nullPtr, out nullPtr, 0);

            if (result == 0)
            {
                throw new Win32Exception();
            }

            return (int)result;
        }

        private FileInfo[] ExtractIcon(int iconIndex)
        {
            FileInfo[] outFiles;
            IntPtr largeIconHandle = IntPtr.Zero;
            IntPtr smallIconHandle = IntPtr.Zero;

            try
            {
                uint result = ExtractIconExW(
                    lpszFile: Source,
                    nIconIndex: iconIndex,
                    phiconLarge: out largeIconHandle,
                    phiconSmall: out smallIconHandle,
                    nIcons: 1);

                if (result == uint.MaxValue)
                {
                    throw new Win32Exception();
                }

                using (Icon largeIcon = Icon.FromHandle(largeIconHandle))
                using (Icon smallIcon = Icon.FromHandle(smallIconHandle))
                {
                    outFiles = new[]
                    {
                        new FileInfo(GetPath("largeIcon", iconIndex)),
                        new FileInfo(GetPath("smallIcon", iconIndex))
                    };

                    largeIcon.ToBitmap().Save(outFiles[0].FullName);
                    smallIcon.ToBitmap().Save(outFiles[1].FullName);
                }
            }
            finally
            {
                DestroyIcon(largeIconHandle);
                DestroyIcon(smallIconHandle);
            }

            return outFiles;
        }

        private string GetPath(string name, int iconIndex)
        {
            return Path.Combine(
                Destination,
                string.Format("{0}-{1}-{2}.bmp", Source, name, iconIndex));
        }
    }
}
'@ -PassThru -ReferencedAssemblies $refAssemblies | Import-Module -Assembly { $_.Assembly }

usage.md

Uses ExtractIconExW function to extract icons from libraries. This function should be compatible with both, Windows PowerShell 5.1 and PowerShell 7+. It will extract both icons, large and small, from a given index (-InconIndex). The function outputs 2 FileInfo instances pointing to the created icons given in -DestinationFolder. If no destination folder is provided, the icons will be extracted to the PowerShell current directory ($pwd).

# Extracts `shell32.dll` icon index 0 to PWD
Invoke-ExtractIconEx shell32.dll -Index 0

# Extracts `user32.dll` icon index 1 and 2 to a specified path
Invoke-ExtractIconEx user32.dll .\pathto\destinationFolder -Index 1, 2

# Extracts ALL icons from `shell32.dll` to PWD
Invoke-ExtractIconEx shell32.dll