@jbacelar
Your solution is pretty handy, easy to implement (using snippets) and very precise.
Again, thank you for a clear proof on how to do it. As I had used before a "plain svg" file produced by Inkscape, I noticed that Inkscape kept repeating the font-family name for each line of text. And I thought that THIS was necessary for svg text files. Another wrong idea discarded.
Also I thought wrongly that it was necessary to write the text on the transparent part of a png. I did some more tries, and I realize now that it works as well with plain jpg files.
Does the size of the viewbox concerns only the size of the image or the intended size of the svg as a whole (I mean including text space)?