Path aliasing feature.

imagepicker does not build nodes, it provides the means to add images to existing node types, pages, stories, blogs whatever. Nodes already have aliasing available.

If an image is the central point of a node it's probably better to use the image module or one of its derivatives

SEOs only look at the domain part of an image url to check wether the image is from the same domain and not 'borrowed' from elsewhere so I see little point in an additional layer of complexity with no benefit. This is why large sites with a dedicated image server use a subdomain in the image url, it keeps the SEOs happy.

The reason for using the uid of the user in the path is because if the user changed their name they would lose all their images. This did happen, that's why the change was made.

If you really don't like the path you can change it but you will need to understand unix file permissions and/or the use of apache mod_rewrite.

HTH