I think I give you 1 token to tell me how to get them nice all in one artwork pics. Damn Ima noob.
Two ways. You can always work something out with me to take the screenshots from your steam profile page, make the image, and give it to you. Or, you can do what I do as described below.
I start by taking screenshots (of course, by hitting F12), with gear equipped on a character so none of the values are red due to being inferior to current gear.
I then switch to steam, and hit view->screenshots. Can't remember if at this point if you have to change the pulldown menu to "Dungeon Defenders", but there should be a button then at the bottom labeled "Show on Disk". Clicking that pulls up the JPEG files on your local hard drive.
I then start up a picture/photo editor. I use Photoshop, but if you don't have that, you could use anything. There's a program called gimp which is free and would do everything you need.
I edit each screenshot I took, cropping them down to just the area showing the item.
I create a new large image (I recommend starting with width 1000px, and height however long you need.) (The picture in this post has height 3300 px.)
I copy each of the cropped "snippets" into this file, lining them up correctly. I use a background color of R196/G168/B131, which I believe from the background color on the item windows - I found this looked nicer than a white background.
I create the text of item # and short description using color R0/G0/B255, which seems to stand out nicely.
I then flatten the image, and post it to an image hosting site. (On this post, I used imgur.com) Make sure if your image hosting site asks you about resizing, that you choose do not resize. Otherwise it'll be so small...
You then need to find the image's web address on that image hosting site. Depending on the site, they'll call it something diffrent. imgur.com calls it "Direct Link". You have to find the one that when you copy that web address into a browser, that just your image shows up -- with nothing on the screen about the image hosting site like their name/logo/buttons/etc.
In a post here, you can click the image button when making a post, and put the URL of the image you just got to have it show up in the thread itself.
Takes a little bit of work. Helps that I've used photoshop for so many years. I can do it in a few minutes, and I figure it increases chance of selling an item and/or getting more for it, since it eliminates most of the work a buyer has to do to look at it.
P.S. Right now I'm getting some error codes from imgur.com - if you get an error, it's likely on their end. You can also use postimage.org, imageshack.us, or tinypic.com. I think one of these doesn't shop up when linked to in a thread, but I can't remember which one it was. I just switched the image over to imageshack.us, since imgur.com is giving errors. They require registration via email, but it's a free account still.