Hi, you will need to you the function gtk_button_set_image_position() to set the position of the image. This was introduced in GTK 2.10. See
http://developer.gnome.org/gtk3/stable/GtkButton.html#gtk-button-set-image-positionThis is a very minimal example showing this.
Code:
/*
* compile with gcc example.c -o example `pkg-config --libs --cflags gtk+-3.0`
*/
#include <gtk/gtk.h>
int main(int argc, char* argv[])
{
GtkWidget *window;
GtkWidget *button;
gtk_init(&argc, &argv);
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
button = gtk_button_new_from_stock(GTK_STOCK_OK);
gtk_button_set_image_position(GTK_BUTTON(button), GTK_POS_TOP);
gtk_container_add(GTK_CONTAINER(window), button);
g_signal_connect(window, "destroy", gtk_main_quit, NULL);
gtk_widget_show_all(window);
gtk_main ();
return 0;
}