- preg_replace: documentation ( source)
<?php
$u = 'http://dev.upload.amiteris.ru/FSfdQOwE0c/image.jpg;width=1072;height=804;mode=crop;anchor=middlecenter;autorotate=true;quality=90;scale=both;progressive=true;encoder=freeimage';
$imageUrl = preg_replace('/\[?;].*$/s', '', $u);
echo $imageUrl;