you could use css to overlay your text on top of an image.... something like this:

<div class="image-with-text">
<img src="your-image.jpg" alt="a nice image" />
<h6>Sweet sweet text</h6>
</div>

.image-with-text{position:relative}
.image-with-text h6 {display:block; position:absolute; bottom:0; background: rgba(255,255,255,0.8)}

the xslt will be something along the lines of:

<div class="image-with-text">
<img>
<xsl:attribute name="src">
<xsl:value-of select="umbraco.library:GetMedia($img0,'false')/data [@alias = 'umbracoFile']" />
</xsl:attribute>
<xsl:attribute name="alt">
<xsl:value-of select="umbraco.library:GetMedia($img0,'false')/@nodeName" />
</xsl:attribute>
</img>
<h6><xsl:value-of select="umbraco.library:GetMedia($img0,'false')/@nodeName" /></h6>
</div>

I hope that helps

-Tim