If you want to embed any photo from flickr to your website or forum, you can embed any flickr photo by hotlinking it. To hotlink flickr photo do following
1. See the desired photo at flickr.com with desired size
2. Right click on photo, click on property
3. select the location URL of Image something like http://farm1.static.flickr.com/170/4459.jpg
4. Copy URL and put that URL at in this code- <img src=”URL”>
5. Copy this code and paste it where you want to get flickr photo.
Remeber that it may not be good practice to put others work at some different forum or website. So its better to mention the source also, and you should give the flickr link (source) for that photo.