Miguel, first of all, thank you for this great project that makes working on more advanced projects on easybook a piece of cake.
The ImageExtra plugin checks for the presence of a '?' on the image string to apply the str_replace for 'images/', so if I just use ![text](images/figure_5.8.png)
it won't match and the build will show a warning:
[WRN] Can't open input file: No such file or directory (/tmp/trefoil/easybook_pdf/images/images/figure_5.8.png)
But if I use ![](images/figure_5.8.png?class="wide")
it will apply the str_replace and everything's good.
An else on the preProcessImages function should resolve it. :) Would you like a PR?