I just bought this picture on ebay. It is undoubtedly from 1920 and clearly shows the pigmented lesion over FDR's left eye. It is the earliest it can be seen (and believe you me I've looked at thousands of photos). The earliest prior photo is from TIME Magazine in 1923.
As you can see it is quite benign appearing at this time and far less noticeable than the mole on his opposite cheek. Twenty-five years later it killed him, from a bleed into a brain metastasis.