retrieve thumbnails

is there a way to retrieve a thumbnail like a normal image?

now i use this link to visualize the img:
http://cdn.kaltura.com/p/4/thumbnail/entry_id/movie_id/width/182/height/...
and to retrive the image:
" alt="Thumbnail" />

but the problem is that certain thumb arrive, certain no and i must try changing the /p/4/ value.

there's a better way? it's a important thing for kaltura i think