i have the same problem 3 days ago, i find a solution, you must generate a .htaccess file from backoffice after you put friendly url !! be aware, if you have apache server, you must activate from apache conf. file, utilization of htaccess !! the problem with image is because they load`s from some path (exemple yourdomain.com/img/picture-medium-9.jpg) and now, the user friendly alterate this path !! this staf generate prestashop when i generate htaccess file (i have an old version of presta 1.3)
# URL rewriting rules
RewriteRule ^([a-z0-9]+)\-([a-z0-9]+)(\-[_a-zA-Z0-9-]*)/([_a-zA-Z0-9-]*)\.jpg$ /img/p/$1-$2$3.jpg [L,E]
RewriteRule ^([0-9]+)\-([0-9]+)/([_a-zA-Z0-9-]*)\.jpg$ /img/p/$1-$2.jpg [L,E]
RewriteRule ^([0-9]+)(\-[_a-zA-Z0-9-]*)/([_a-zA-Z0-9-]*)\.jpg$ /img/c/$1$2.jpg [L,E]
RewriteRule ^lang-([a-z]{2})/([a-zA-Z0-9-]*)/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$3&isolang=$1$5 [L,E]
RewriteRule ^lang-([a-z]{2})/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$2&isolang=$1$4 [L,E]
RewriteRule ^lang-([a-z]{2})/([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /category.php?id_category=$2&isolang=$1 [QSA,L,E]
RewriteRule ^([a-zA-Z0-9-]*)/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$2$4 [L,E]
RewriteRule ^([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$1$3 [L,E]
RewriteRule ^([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /category.php?id_category=$1 [QSA,L,E]
RewriteRule ^content/([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /cms.php?id_cms=$1 [QSA,L,E]
RewriteRule ^([0-9]+)__([a-zA-Z0-9-]*)(.*)$ /supplier.php?id_supplier=$1$3 [QSA,L,E]
RewriteRule ^([0-9]+)_([a-zA-Z0-9-]*)(.*)$ /manufacturer.php?id_manufacturer=$1$3 [QSA,L,E]
RewriteRule ^lang-([a-z]{2})/(.*)$ /$2?isolang=$1 [QSA,L,E]