How can you crop an image and output from a Matrix field?
When you call .first on an Asset field, that's going to return an AssetFileModel.

Change the relevant part of your code to this:

{# grab the first image #}
{% set image = block.image.first() %}

{# link to the full sized version #}
&lt;a href="{{ image.getUrl('thumb') }}"&gt;

    {# generated the transformed thumbnail version #}
    &lt;img src="{{ image.getUrl('thumb')}}" alt="{{ block.alt }}" width="{{ image.getWidth('thumb') }}" height="{{ image.getHeight('thumb') }}"&gt;

    &lt;div id="lightbox-title"&gt;
        &lt;h2&gt;{{ block.imageTitle }}&lt;/h2&gt;
        &lt;p&gt;{{ block.imageContent }}&lt;/p&gt;
    &lt;/div&gt;
&lt;/a&gt;