You can post very large images. However, there is a limit on depth (or weight, if you prefer). The reason is that a computer screen can usually show a pixel depth of 300 dpi only. In other words, a picture of 300 dpi looks exactly the same on your screen as a picture of 1200 dpi your scanner can produce, but the 1200 dpi picture takes roughly four times as much place. A coin site is picture rich, pictures, not text determine how much place the site takes on the server and that determines how much you pay. In conclusion, the restriction on picture depth does not diminish the quality of the picture on your screen, but it does save an important amount of money.
So how do you diminish pixel depth? With a free or paid application or with a free web site. First of all, think of converting any .PNG file to a .JPG file. Next, there is a list of options
here. You can post your questions on
this board.
A further option is to post your image elsewhere on the net and link it to your post (embedding). However, if in due time you do anything that affects the link, your picture will disappear here. You can see the damage that does in some older threads. It may be a solution while you find out which other option works for you, though.
Peter