Mine

Gdk.Pixbuf icon = image.Pixbuf;
Gdk.Pixbuf emblem = WidgetFu.LoadMimeIcon (parent_mime_type, 24);

if (emblem == null)
	return;

emblem.Composite (icon, 
		  0,                                // dest_x
		  0,                                // dest_y
		  emblem.Width,                     // dest_width
		  emblem.Height,                    // dest_height
		  0,                                // offset_x
		  0,                                // offset_y
		  1, 1,                             // scale
		  Gdk.InterpType.Bilinear, 255);


#6  0xb665a129 in composite_line (weights=0x86c2900, n_x=2, n_y=2,
    dest=0xb552f31c "", dest_x=0, dest_end=0xb552f378 "", dest_channels=4,
    dest_has_alpha=1, src=0x86c4450, src_channels=4, src_has_alpha=1,
    x_init=0, x_step=65536, src_width=24, check_size=0, color1=0, color2=0)
    at pixops.c:467
#7  0xb665ba83 in pixops_process (dest_buf=0xb552f31c "", render_x0=0,
    render_y0=0, render_x1=24, render_y1=24, dest_rowstride=128,
    dest_channels=4, dest_has_alpha=1, src_buf=0xb211dc18 "", src_width=24,
    src_height=24, src_rowstride=96, src_channels=4, src_has_alpha=1,
    scale_x=1, scale_y=1, check_x=0, check_y=0, check_size=0, color1=0,
    color2=0, filter=0xbfde51ac, line_func=0xb6659f00 <composite_line>,
    pixel_func=0xb6659e00 <composite_pixel>) at pixops.c:1146
#8  0xb665ceb2 in _pixops_composite (dest_buf=0xb552f31c "", render_x0=0,
    render_y0=0, render_x1=24, render_y1=24, dest_rowstride=128,
    dest_channels=4, dest_has_alpha=1, src_buf=0xb211dc18 "", src_width=24,
    src_height=24, src_rowstride=96, src_channels=4, src_has_alpha=1,
    scale_x=1, scale_y=1, interp_type=PIXOPS_INTERP_BILINEAR,
    overall_alpha=255) at pixops.c:1556
#9  0xb6656943 in IA__gdk_pixbuf_composite (src=0x86c7438, dest=0xb552f31c,
    dest_x=0, dest_y=0, dest_width=24, dest_height=24, offset_x=0, offset_y=0,
    scale_x=1, scale_y=1, interp_type=GDK_INTERP_BILINEAR, overall_alpha=255)
    at gdk-pixbuf-scale.c:139


Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1210419008 (LWP 21164)]
0xb6661129 in composite_line (weights=0x86c2438, n_x=2, n_y=2,
    dest=0xb553471c "", dest_x=0, dest_end=0xb5534778 "&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;&#65533;",
    dest_channels=4, dest_has_alpha=1, src=0x86c3e70, src_channels=4,
    src_has_alpha=1, x_init=0, x_step=65536, src_width=24, check_size=0,
    color1=0, color2=0) at pixops.c:467
467                   dest[0] = 0;