Hello, *ezequiel and welcome to the forum. You cannot publish directly any file in the web categories, due to this web is based in quality and preserve the material as near as possible of the originals, and not in adding many edited boxes.
If you want that you box will be added to the web, you need edit as near as possible to original one, basically scan or editing above real box, and send it to Contribute zone-->Drop files zone in the upper menu.
Then it will be checked for an admin and reject or added to the web depending if it is near to real box.
If you want publish your boxes as custom boxes, you can share like now in the forum, and put the link to original size file (for example in archive website), and people can comment and help you to improve the results. Like you have done.
Sadly, I must warn you that editing a box is not as easy as putting paint in a few colors and it takes time to learn, but we can learn together on the web.
For example, the cover of Captain Tsubasa III, when compared to the original, shows that the colors don't match the originals, the images aren't very high-quality, and the colors aren't clear. For example, the logo subtitle letters are light blue, not white. The four-color SFC logo isn't as close to the top, the colors of the flaps and box don't match, etc.
The label is a very low-quality image; only an actual 600 dpi scan is acceptable for labels, not photos. This assets will not be accepted I think.
Thank you so much for your collaborations and I hope that you continues improving your work.
Regards.