Photodropper seems to set to every visitors these two cookies:
pdrp_mark_install (value '1') and pdrp_mark_welcome (value '1').
This is bad practice for several reasons:
- these cookies are sent along every single http request the visitors browser make, adding for extra traffic
- these cookies burst caches in vain
I particular the latter point is a big issue. When any proxies or caches in the server end or in closer to the visitor tires to cache some of the files transferred over http, these cookies stop it from happening. Even though the cache and expire headers are OK, the mere presence of cookies makes proxies assume that the content varies for visitors who have different values in the cookies, thus nothing is actually cached.
Please consider alternative ways to do what you do. If I'd know what the purpose of these cookies is, I could give some implementation suggestions.
I think you could maybe manage without setting cookies at all for regular visitors and set the cookies only for site admins. For site admins you could also even save you stuff in the PHP session store and avoid Photodropper-specific cookies.