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;

namespace ExtractIconEx
{
    [Cmdlet(VerbsLifecycle.Invoke, "ExtractIconEx")]
    [OutputType(typeof(FileInfo))]
    public sealed class InvokeExtractIconEx : PSCmdlet
    {
        private string _defaultSource = "shell32.dll";

        [Parameter]
        [ValidateNotNullOrEmpty]
        public string SourceLibrary
        {
            get
            {
                return _defaultSource;
            }
            set
            {
                _defaultSource = value;
            }
        }

        [Parameter(Position = 0)]
        [ValidateNotNullOrEmpty]
        public string DestinationFolder { get; set; }

        [Parameter(Position = 1)]
        public int IconIndex { get; set; }

        protected override void EndProcessing()
        {
            if (string.IsNullOrEmpty(DestinationFolder))
            {
                DestinationFolder = SessionState.Path.CurrentFileSystemLocation.Path;
            }

            try
            {
                FileInfo[] fileInfos = ShellApi.ExtractIcon(
                    SourceLibrary,
                    GetUnresolvedProviderPathFromPSPath(DestinationFolder),
                    IconIndex);

                WriteObject(fileInfos, enumerateCollection: true);
            }
            catch (Exception e)
            {
                WriteError(new ErrorRecord(
                    e, "IconExtractError", ErrorCategory.NotSpecified, null));
            }
        }
    }

    internal sealed class SafeIconHandle : SafeHandle
    {
        [DllImport("user32.dll")]
        private static extern bool DestroyIcon(IntPtr hIcon);

        internal SafeIconHandle() : base(IntPtr.Zero, true)
        {

        }

        public override bool IsInvalid
        {
            get
            {
                return handle == IntPtr.Zero;
            }
        }
        protected override bool ReleaseHandle()
        {
            return DestroyIcon(handle);
        }
    }

    internal static class ShellApi
    {
        [DllImport(
            "shell32.dll",
            CharSet = CharSet.Unicode,
            SetLastError = true)]
        private static extern uint ExtractIconExW(
            string szFileName,
            int nIconIndex,
            out SafeIconHandle phiconLarge,
            out SafeIconHandle phiconSmall,
            uint nIcons);

        private static void ExtractIconEx(
            string fileName,
            int iconIndex,
            out SafeIconHandle iconLarge,
            out SafeIconHandle iconSmall)
        {
            if (ExtractIconExW(fileName, iconIndex, out iconLarge, out iconSmall, 1) == uint.MaxValue)
            {
                throw new Win32Exception();
            }
        }

        internal static FileInfo[] ExtractIcon(
            string source,
            string destinationFolder,
            int iconIndex)
        {
            SafeIconHandle largeIconHandle;
            SafeIconHandle smallIconHandle;
            ExtractIconEx(source, iconIndex, out largeIconHandle, out smallIconHandle);
            FileInfo[] outFiles;

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

                largeIcon.ToBitmap().Save(outFiles[0].FullName);
                smallIcon.ToBitmap().Save(outFiles[1].FullName);
            }

            return outFiles;
        }

        private static string GetPath(
            string source,
            string destinationFolder,
            string name,
            int iconIndex)
        {
            return Path.Combine(
                destinationFolder,
                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 to PWD
Invoke-ExtractIconEx -InconIndex 1

# Targeting a different library
Invoke-ExtractIconEx -SourceLibrary user32.dll -InconIndex 1

# Using a different target folder
Invoke-ExtractIconEx path\to\my\folder -InconIndex 1