If you combine and art graphic program (Gimp, Photoshop,etc..) with Altana viewer you can get all kinds of things done. Thats what I use at least.

Altana Viewer: http://longtear.hp.infoseek.co.jp/altanaview_en.html

Some stuff i've done (Lots more on my Profile): http://myffxi.com/blog/view/id_364/title_ffxi-psp/

If you have any questions or need help send a message. I'd be glad to teach you or help you. Take Care!

Well the larger images are considered signatures. For example:

But the smaller square images, such as the one to the right of this post, are usually called avatars or display pictures. Usually people like myself will use computer programs like Photoshop to make these images. Hope that answers your question. ^^

Ryuki can help you with that.^^ They're called Signatures.