Of course the value will depend on many variables. A typical postcard should be worth $5 if it was mailed from a soldier overseas. A postcard with a photo may be worth more. Some cards with a commercial Logo such as Coca-Cola might have a special interest to collectors. I have a post card mailed from Stalag IIb that has a German stamp and an ink stamp of the prison camp and I would expect it to be worth $25 or as much as $40.
It matters who they are of and how old they are.
Hard to say without more information. There are literally dozens of varieties of the early post cards. Most are going to be worth a few cents if they are used. Unused they might bring a few dollars. You'll need a lot more info to figure it out. Most stamp catalogs will have post office post cards listed in the back of the book.
Yes they can certainly have value. There is going to have a lot more detail to fully identify the post card. Use of a stamp catalog, looking under postal stationary, in the back of the book, to identify the card. It will also provide a general value.
it is worth up to 100 dollars depending on how old it is
Dates are needed. Post new question.
2 Jack Daniels Playing Cards Black Whiskey Old No.7$4.99* http://www.playwiththegods.com/ideal_collectibles/Advertising-Collecta
no unless they are really old then they would be worth some money
It depends on the dates. Post new question with the dates.
I know you use to be able to do iy, but don't know now
If the stamp has been used, the post office will tell you it is worthless. If a stamp has not been used, they will tell you it is worth whatever is on its face value. The post office will not appraise a stamp for its collectable value.
you can make old christmas cards into pumpkins
The value of 100 year old postcards depends greatly on the subject of the cards and what kind of condition they are in. The value can be anywhere from a few cents up to $100 or even more.