So if you want to contribute your art, which is great, since there is not so much public domain material out there, this is why I made this site, you have to follow some guidelines, since I do want to keep a certain quality, since most free site accumulate a lot of garbage over time. Otherwise you can read a little about how it works.
In general, you should have some experience of what you are doing, but you don't have to be professinal.
The art-section is divided into several subcategories:
"Texture Photos": This is where photos belong, that were made with the intention to make textures out of them. (use content Type "Photo" for these)
"Regular Photos": Other photos belong here, like artistic or scenery photos. (use content Type "Photo" for these)
"Textures": This is where edited versions of the photos belong, like already made seamless, or alpha masked and other improvements, like equalized lighting and so on. Also zip files can be uploaded there, this is intended to pack a full material with all its layers into it, that can be used in a game engine, for example diffuse, normal and specular map make a material, this can be zipped up and attached to the texture, the picture file of the texture should be the base image that was used to create the material, if there should be one. (use content Type "Texture" for these)
"Synthetic Textures": The same as textures, but only for artificially created textures, not realistic ones from photos, like painted or rendered ones. (use content Type "Texture" for these)
"3D-Models": For 3D-models made from the textures or 3D-models to render textures from. (use content Type "3D-Model" for these)
If you want to submit photos, you should take care on a few points.
The photos itself should be sharp and suitable for making textures, if they are supposed for that category.
Image size and quality: Image size in disk space should be around 3 MB, since many cameras save in unnecessary big files.
The resolution should be around 10 Megapixels, far more or far less does not make sense, many sites offer 20 Megapixel or more resolution photos, but there is no real visible difference, this is mostly marketing.
The JPG-quality should be around 85, inbetween 80 and 90, over 90 there is no visible improvement also, but it rapidly increases the filesize and under 80 compression artifacts start to appear. Best practice is likly to set your camera to default JPG-quality, then it will likely chose something in that range, while the "fine" option, will likely chose something over 90, which is not really necessary.
And avoid resaving JPG-files too often, one time conversion is okay, if you decide to shoot with very high settings.
The files should be named something individually, this makes finding and categorizing easier. I use a batch rename to add my initials in front of the filenames.
Then I use the Exiftool to remove the Exif-data from the photos, since in my case it reduces file size by 10-20%, so something big is saved in there I do not really know of and then I add back in a comment with where the file is from, author name and the license, to help people keep track of origin and license. You don't have to do that, but I find it nice and in general it is a good practice to remove the Metadata from your pictures before releasing them in the internet, because some tools save unwanted information in there, for example most smartphones save GPS data into there and so on, but I hope you use a real camera for the textures, it was just an example.
I add following comment to my photos:
Downloaded from: http://www.duion.com
Author: Christian Femmer (replace with your name or pseudonym)
License: CC0 (Public Domain)
I decided to do it like this to help people keep track where the image is from, the license and from who it is, if they decide to give credit anyway. You don't have to do it, but it would be better, at least the license part should be like that, so you have to chose CC0 always, for the name you can use your full name or any pseudonym, both is okay and the link is to assure people where it is from originally. So you understand my intention behind this.
The Exiftool command line for this is:
exiftool -all= -Comment"<=comment.txt" yourimagefolder
Note, you have to be one directory below the folder with your images you want to remove the Metadata and exchange "yourimagefolder" with your foldername, also you need to create a comment.txt file where you write in the comment that should be added to the images, like the example above (in the folder below the image folder)
This all may sound complicated, but I found this to be the best tool for manipulating Metadata.
Uploading content: To upload content, in the upper right corner there is a button "Add Content" this will lead you to the menu, where you can add content. Chose "Bulk Upload Photos" for texture photos and regular photos.
In the upload form, don't enter a filename, since it will automatically create a title named after the filename, this is also why you should have individual filenames, numbers are added in case something is dublicated, but that is not nice.
Then you can drag and drop your files into the upload window and can press upload, while it is uploading you have to chose a category (if the category does not exist yet, ask me, so I will create it first), so you best only add a bunch of images of the same category at the same time. Then you can add a description or some search tags for search engines, but this is optional. Remember that this description is added to every photo you upload in this session, but you can change it individually afterwards, but if you upload bunches of similar photos at once, it saves you time. The author field is not necessary, it is just in case. I stopped adding author name, but it could be used if uploader and author are different persons.
If you are done, you can click "Generate Node entities" and it will create the entries, but look if the uploads are finished. Alternatively, you can not press the "start upload" button and fill out the fields before that and then hit "Generate Node entities" then he will start uploading and generate the entries afterwards, so you don't have to wait in front of the computer for it.
Other categories than "Texture Photos" or "Regular Photos" need you to chose the appropriate content type from the "Add Content" menu and currently have no batch functionality, like with the photos, so every entry needs to be created manually.
Don't mix your uploads too much, since all items are sorted by time of upload, so if you upload similar bunches, it looks nicer in the timeline.