Thanks for reply
It's easy with an image hosting web, but the pictures can dissaper anytime or some users can't see and for this reasons i prefer to attach on forum.

Me too.
Just be mindful of the size of images you want to upload to Dave's server AND the the time and BW it will take for a large (Mb) image to download when embedded in your posts. Not all members have fast internet connections and big images can take an age to download, the thumbnails not though.
Use big images when great detail is required however in most cases 100 Kb is plenty to see enough detail.
As others have said use the URL of the thumbnails to embed images and ensure they're within the img tags. (Insert Image)