Your photograph is a tintype (ferrotype). Tintypes are basically the negative, subsequent copies are not made, so each photo is a unique image. To make multiple images, a multi-lens camera was used to expose several smaller photos on a plate, then the plate was cut apart by hand like old school photos. There is much information on line about the process.
Size does matter to collectors. This looks like one of the the larger sizes :
Half plate= 5" x 7" / 4.5" x 6.5" (smallest size at least 4.5")
Full plate/Whole plate: 6.5"+ x 8.5+"
Mammoth plate: 7.5 x 10; 10 x 12, 10 x 14 (one side at least 10")
While most cameras held conventional sizes, there was some variation. Also plates were trimmed either by the photographer or to fit a frame, which explains the jagged edge on your photograph.
As stated, the image is hand colored or painted. These were common enough at the time, a pair of husband and wife often hung over the mantel. Collectors look for unusual details, hat, jewelry, foliage or color patterns, full body, furniture, clothing details and youth (the larger portrait photos are usually of older people).
Your image lacks those exceptions, placing it toward the lower price end, but it still retains a folk art appeal and the hair style is of the time. Do not try to clean or alter in any way -you will inevitably ruin it.
When mailing add layers of heavy cardboard as these plates are very easily bent and dented in the mail.
