This program will create an offscreen(invisible) webkit-web-view, and take a screenshot of the loaded document, the document/URL is passed as a command line argument to the program

webview-snapshot.c

#include <gtk/gtk.h>
#include <webkit/webkit.h>


static void destroyWindowCb(GtkWidget* widget, GtkWidget* window);
static gboolean closeWebViewCb(WebKitWebView* webView, GtkWidget* window);


static void 
webkit_render_cb(WebKitWebView *webview,
                 WebKitWebFrame *webframe,
                 gpointer data)
{
    cairo_surface_t *surface = webkit_web_view_get_snapshot(webview);
    cairo_surface_write_to_png(surface,"img.png");
}


int main(int argc, char* argv[])
{
    // Initialize GTK+
    gtk_init(&argc, &argv);

    // Create an 800x600 offscreeen window that will contain the browser instance
    GtkWidget *main_window = gtk_offscreen_window_new();
    gtk_window_set_default_size(GTK_WINDOW(main_window), 800, 600);

    // Create a browser instance
    WebKitWebView *webView = WEBKIT_WEB_VIEW(webkit_web_view_new());

    // Create a scrollable area, and put the browser instance into it
    GtkWidget *scrolledWindow = gtk_scrolled_window_new(NULL, NULL);
    gtk_scrolled_window_set_policy(GTK_SCROLLED_WINDOW(scrolledWindow),
            GTK_POLICY_AUTOMATIC, GTK_POLICY_AUTOMATIC);

    gtk_container_add(GTK_CONTAINER(scrolledWindow), GTK_WIDGET(webView));

    // Set up callbacks so that if either the main window or the browser instance is
    // closed, the program will exit
    g_signal_connect(main_window, "destroy", G_CALLBACK(destroyWindowCb), NULL);
    g_signal_connect(webView, "close-web-view", G_CALLBACK(closeWebViewCb), main_window);

    //When the load is finished we grab a screenshot of the loaded document.
    g_signal_connect(webView,"document-load-finished",G_CALLBACK(webkit_render_cb),NULL);
    g_signal_connect(webView,"document-load-finished",G_CALLBACK(destroyWindowCb),NULL);

    // Put the scrollable area into the main window
    gtk_container_add(GTK_CONTAINER(main_window), scrolledWindow);

    // Load a web page into the browser instance
    webkit_web_view_load_uri(webView, argv[1]);

    // Make sure that when the browser area becomes visible, it will get mouse
    // and keyboard events
    gtk_widget_grab_focus(GTK_WIDGET(webView));

    // Make sure the main window and all its contents are visible
    gtk_widget_show_all(main_window);

    // Run the main GTK+ event loop
    gtk_main();

    return 0;
}


static void destroyWindowCb(GtkWidget* widget, GtkWidget* window)
{
    gtk_main_quit();
}

static gboolean closeWebViewCb(WebKitWebView* webView, GtkWidget* window)
{
    gtk_widget_destroy(window);
    return TRUE;
}