>>20021996I'll use this one
>>20020114 and
>>20020323 this one as examples.
In the first case, the original image can be found here.
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=38892863As you can see, the image is small and has a weird "stack of papers" effect. The papers means it's an image set, and if you click on the image you'll open that set of images. While in the image set viewer, most images are at their full size. However, for really really big pictures you'll need to click on the arrows to the left of the image, that will expand the image to its full size. Sometimes clicking the arrows isn't necessary, but it's usually a good precaution.
In the second, case, the original image can be found here.
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=38180735On the top of the image description, you'll see that the resolution says "2960×2100", but the actual image itself is much smaller. Like the last case, you have to click on it to open the full size in another tab, but since this isn't an image set you just go straight to the full sized image.
If you're wondering how I found the source of the pictures, use this:
http://saucenao.com/ or
http://saucenao.com/tools/ 
