Uploading background I created into the library for others to use?

FF can make and render any image size and not only 600x600 that is only the default preview size

Sorry that I may not understand correctly what you want to do

1 - Do you want to submit to the library a filter you have made that creates this background you have shown here?

2 - Or do you want to include this background as an image inside the filter that you have made, and this background is not made using FF components?

3 - or do you want to upload the background you have made to the forum for other to use it ?

ANSWER to 1

If you answer yes to question 1, then you only have to follow the FF guidelines

https://www.filterforge.com/more/guidelines.html

And when you are ready and finished with your filter go to the submit wizard and it will tell what you need to do

https://www.filterforge.com/more/help/...izard.html

ANSWER TO 2

I ask this because if the answer is yes to the scond question, then The FF library does not allow you to include any kind of your own custom images whatever it may be inside a filter that you want to submit to the FF library, you can only include built-in images

But, you can submit the filter to the library and then when available, you can put your own custom background on the filter page for anyone to download it and use with the filter

I do not know if you can upload a filter with a custom background to the forum

ANSWER TO 3

If you just want to upload a background for others to use

In the forum you can upload the background at ANY SIZE that you may want that is below 1000 Kb