set as image as header CollapsingToolbarLayout on Collapse

First create your them with this link, Transparent toolbar and set it as theme of your activity

xml code is as follows,

<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">

<android.support.design.widget.AppBarLayout
    android:id="@+id/app_bar_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    android:fitsSystemWindows="true">

    <android.support.design.widget.CollapsingToolbarLayout
        android:id="@+id/collapsing_toolbar"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_scrollFlags="scroll|exitUntilCollapsed"
        app:contentScrim="?attr/colorPrimary"
        app:expandedTitleMarginStart="48dp"
        app:expandedTitleMarginEnd="64dp"
        android:fitsSystemWindows="true">

        <ImageView
            android:id="@+id/image"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:scaleType="centerCrop"
            android:fitsSystemWindows="true"
            app:layout_collapseMode="parallax"/>

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
            app:layout_collapseMode="pin" />

    </android.support.design.widget.CollapsingToolbarLayout>

</android.support.design.widget.AppBarLayout>

and in activity,

 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        collapsingToolbarLayout = (CollapsingToolbarLayout) findViewById(R.id.collapsing_toolbar);
        collapsingToolbarLayout.setTitle(itemTitle);

Try removing the contentScrim attribute from CollapsingToolbarLayout.