Welcome to Mobileread....
Have you seen the
Author Self-Promotion Forum ... and also the
Writers' Corner ... Just two of the many gems we have on board
...
The first one perhaps of more use to a wider audience than this part of Mobileread...Covers can be uploaded, use attachment under "Go Advanced".
A signature line will also be a place to put covers, but you'll have to wait for around 10 posts and one week since registration before you can get that as an option.
Note the FAQs dictate what you can and can't do with signature and image sizes.
Welcome....