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function oci_adminbar_logo() {
	echo '<a href="' . get_blog_option( 1, 'siteurl' ) . '">&lt;img id="admin-bar-logo" src="' . apply_filters( 'bp_admin_bar_logo_src', site_url( MUPLUGINDIR . '/bp-core/images/oci_home.gif' ) ) . '" alt="' . apply_filters( 'bp_admin_bar_logo_alt_text', __( 'BuddyPress', 'buddypress' ) ) . '" /&gt;</a>';
}
remove_action('bp-adminbar-logo','bp_adminbar_logo');
add_action('bp-adminbar-logo','oci_adminbar_logo');

Note: replace /bp-core/images/oci_home.gif with an image of your liking.