【运行效果】

【对话框资源】

在对话框资源中，图像控件为：

其中ID为IDC_BMP，Type为Bitmap：

【C++代码】
#include <tchar.h>
#include <Windows.h>
#include <CommCtrl.h>
#include <gdiplus.h>
#include <winhttp.h>
#include "resource.h" // 资源头文件

// 启用XP风格
#pragma comment(lib, "Comctl32.lib")
#pragma comment(linker, "\"/manifestdependency:type='win32' name='Microsoft.Windows.Common-Controls' version='6.0.0.0' processorArchitecture='*' publicKeyToken='6595b64144ccf1df' language='*'\"")

#pragma comment(lib, "gdiplus.lib")
#pragma comment(lib, "winhttp.lib")
using namespace Gdiplus;

HBITMAP hbmp; // 位图句柄
TCHAR szBmpText[30]; // 提示框的内容

// 加载图像
void LoadPicture(void)
{
    // 连接服务器
    HINTERNET hSession = WinHttpOpen(L"My Test", NULL, NULL, NULL, NULL);
    HINTERNET hConnect = WinHttpConnect(hSession, L"zh.arslanbar.net", INTERNET_DEFAULT_HTTP_PORT, NULL);
    HINTERNET hRequest = WinHttpOpenRequest(hConnect, L"GET", L"Files/TopicImages/2012-7/8_2012-7-13_121400_609-318482.jpg", NULL, NULL, NULL, WINHTTP_FLAG_REFRESH);
    WinHttpSendRequest(hRequest, NULL, NULL, NULL, NULL, NULL, NULL);
    WinHttpReceiveResponse(hRequest, NULL);

    // 下载图像到内存中
    HGLOBAL hMem = NULL;
    char *content = NULL;
    DWORD dwSize;
    DWORD dwRead = 0;
    DWORD dwBufSize = 0;
    while (WinHttpQueryDataAvailable(hRequest, &dwSize), dwSize > 0)
    {
        if (hMem == NULL)
            hMem = GlobalAlloc(GMEM_MOVEABLE, dwSize);
        else
            hMem = GlobalReAlloc(hMem, dwBufSize + dwSize, GMEM_MOVEABLE);
        content = (char *)GlobalLock(hMem);
        WinHttpReadData(hRequest, content + dwBufSize, dwSize, &dwRead);
        GlobalUnlock(hMem);
        dwBufSize += dwSize;
    }
    WinHttpCloseHandle(hRequest);
    WinHttpCloseHandle(hConnect);
    WinHttpCloseHandle(hSession);

    // 转换为Stream对象并创建位图对象
    IStream *is;
    CreateStreamOnHGlobal(hMem, TRUE, &is);
    Bitmap bmp(is);
    is->Release();

    // 获得位图句柄
    bmp.GetHBITMAP(Color::White, &hbmp);
    _stprintf_s(szBmpText, TEXT("Size: %ux%u"), bmp.GetWidth(), bmp.GetHeight());
}

// 创建提示框
void CreateTooltip(HWND hDlg)
{
    HINSTANCE hInst = (HINSTANCE)GetWindowLongPtr(hDlg, GWLP_HINSTANCE);
    HWND hwndTip = CreateWindow(TOOLTIPS_CLASS, NULL, WS_POPUP | TTS_ALWAYSTIP, 0, 0, 0, 0, hDlg, NULL, hInst, NULL);

    TOOLINFO ti;
    ZeroMemory(&ti, sizeof(ti));
    ti.cbSize = sizeof(TOOLINFO);
    ti.hwnd = hDlg;
    ti.hinst = hInst;
    ti.lpszText = szBmpText;
    ti.uFlags = TTF_SUBCLASS;

    // 获取图像控件相对于对话框的矩形区域
    POINT pt;
    HWND hwndStatic = GetDlgItem(hDlg, IDC_BMP);
    GetWindowRect(hwndStatic, &ti.rect);
    pt.x = ti.rect.left;
    pt.y = ti.rect.top;
    ScreenToClient(hDlg, &pt);
    GetClientRect(hwndStatic, &ti.rect);
    OffsetRect(&ti.rect, pt.x, pt.y);

    SendMessage(hwndTip, TTM_ADDTOOL, NULL, (LPARAM)&ti);
}

INT_PTR CALLBACK DlgProc(HWND hDlg, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    int wmId;
    switch (uMsg)
    {
    case WM_INITDIALOG:
        SendMessage(hDlg, WM_SETICON, ICON_SMALL, (LPARAM)LoadIcon(NULL, IDI_APPLICATION)); // 设置对话框图标
        LoadPicture(); // 当对话框创建时加载图像
        SendDlgItemMessage(hDlg, IDC_BMP, STM_SETIMAGE, IMAGE_BITMAP, (LPARAM)hbmp);
        CreateTooltip(hDlg);
        break;
    case WM_COMMAND:
        wmId = LOWORD(wParam);
        switch (wmId)
        {
        case IDOK:
        case IDCANCEL:
            DestroyWindow(hDlg);
            break;
        }
        break;
    case WM_DESTROY:
        DeleteObject(hbmp); // 当对话框关闭时删除位图句柄
        PostQuitMessage(0); // 退出消息循环
        break;
    }
    return FALSE;
}

int APIENTRY _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow)
{
    // 初始化GDI+
    GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    // 创建并显示对话框
    HWND hDlg = CreateDialog(hInstance, MAKEINTRESOURCE(IDD_DIALOG1), NULL, DlgProc);
    ShowWindow(hDlg, nCmdShow);

    // 消息循环
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    GdiplusShutdown(gdiplusToken);
    return msg.wParam;
}

显示半透明的png图片：
HINTERNET hConnect = WinHttpConnect(hSession, L"assets.onestore.ms", INTERNET_DEFAULT_HTTP_PORT, NULL);
HINTERNET hRequest = WinHttpOpenRequest(hConnect, L"GET", L"cdnfiles/onestorerolling-1602-26000/shell/v3/images/logo/microsoft.png", NULL, NULL, NULL, WINHTTP_FLAG_REFRESH);

在程序中使用GDI+的目的是为了能够直接显示png、jpg、gif等多种图像文件格式。如果直接使用GDI的话就只能显示bmp位图。但实际上网络中几乎不存在bmp位图，基本上都是压缩后的png或jpg等格式。