Unlike many other scoop sites, HuSi allows one to use images in your diaries, comments, and signatures. With this great feature comes great responsibility. Folks abusing this feature by posting inappropriate images can expect to be put in The Hole, or even banned from using images altogether.
To use the Post Images feature, you first have to upload the images. On the right hand navigation bar, right below New Diary is "Your Files". Click on Your Files, and you'll be presented with a HTTP upload page to browse and upload a file. Also on this page will be a list of all the files you've uploaded and some management options. File uploads are not limited to image files only, but images are the only thing that can be embedded in you comments & diaries.
Obviously there are physical limits to what you can upload. No files larger than 200k are allowed, and the maximum you can have stored on the server is around 4MB. There are also controls in place to stop people using the images from outside HuSi. If you link to an image from another server (Hotlinking) you won't get the image you expect.
So upload the pictures you desire and then go write a diary, or a comment. When writing a comment, on the right hand nav bar is a User Files section. There's a drop down box that will list the file(s) you've uploaded, and a button marked "<<Comment" (for comments) or "<<Body" (for stories/diaries). Select the file you want from the drop down and click the button. You will then see text like "((file [121/lava.gif] ))" in your comment area. In this example, 121 is my user ID, and lava.gif is the picture. You shouldn't ever have to edit the file name or user ID. The second set of empty brackets is for labeling the picture.
Preview your diary to make sure it works, and you've now posted an image.
If you want to use the image in your signature, simply copy the ((file )) text from the comment, and put it in your signature area in your User Preferences