Step 1:Click on the small arrow near your post information
Step 2: Image search: iqdb. This will reverse image search for you.
Step 3: Literally the first result is a Sankaku Channel listing. The artists name is listed on the tags at the side.
b-but anon, I've had the file saved on my computer/didn't find it on 4chan. How can I reverse image search if it's not uploaded here already?
Easy. Just google revere image search. If it's a more general image you could use something like TinEye or Google's search function. However for art like this and anime things in general, you're better of using the reverse image tools of image hosts such as danbooru, gelborru, sankaku, etc.
http://sankaku.iqdb.org/http://danbooru.iqdb.org/So to answer your question on who the artist is [spoiler:lit] fuck off, do it yourself[/spoiler:lit]