Comment 4 for bug 1357808

@giuliano69 - I wrote the extension with Inkscape 091 in mind, but it can be used in either version (in 0.48 to prepare files to be used in 0.91, in 0.91 to fix rendering of files created with older versions). If you run it in 0.48, you won't see an immediate visual effect there, whereas in 0.91, the images will be rendered scaled as expected immediately after the extension has been applied.

Steps:
1) install extension
2) open the SVG file in Inkscape 0.91
3) apply the extension (Extensions > Images > Set attribute 'preserveAspectRatio')

The default settings will add the attribute to _all_ images in the current document.