A lot of the issues concerning how far a planitff can go in seeking damages has to do with proving the intent of the coroporation and its officers to willfully defraud or do harm to stockholders, clients or customers. When company officials conspire to cheat any of the above it moves from areas such as product liability (damages limited to assets of the corp) to crimes involving fraud and embezzelment ala Enron, World Com, Tyco etc. When you get into this area state and federal law determine fines and jail time. After that plantiffs can go after personal assets through various civil suit avenues.
In the much smaller realm of selling fine art photographs I don't know what one could be liable for other then replacing a print that may have not been properly finished to archival standards. Most of those types of issues would be covered in purchase agreements with the work.
Untill the amount of income you make would reach the threshold that incorporating makes sense, sole-proprietorship is the simpler and less expensive option.