[LifesGreatestGift]

without an extensive plugin, you could create a custom profile field and users could insert the URL to an image hosted on an image host (photobucket, tinypic etc) and then you could render the image like this

For Posts (postbit/postbit_legacy):

<vb:if condition="$post['fieldx'] != ''">
    <img src="{vb:raw post.fieldx}" alt="" />
</vb:if>

x being the ID of the custom profile field.