If anyone needs an example of the SVG method mentioned above:
Code:
<body style="background-color:black">
<div style="margin:0; padding:0; text-align:center">
<svg xmlns="http://www.w3.org/2000/svg" height="100%" preserveAspectRatio="xMidYMid meet" version="1.1" viewBox="0 0 881 1500" width="100%" xmlns:xlink="http://www.w3.org/1999/xlink">
<image height="1500" width="881" xlink:href="../Images/map.jpg" />
<text text-anchor="middle" x="50%" y="40" style="fill:white; font-size:50px; font-family:serif">Caption</text>
</svg>
</div>
</body>
I have the code set as a template. I just correct the name of the file and the caption, and, if needed, change the font-size, y=, and image dimensions. Remember to add room for the caption to the image/viewbox heights.
Cheers!