Here is one of the ones I have from the collection. It appears to be a photo that's been turned into a post card - as Rik has mentioned being somewhat common in years past. I'm hoping someone can provide some information on the ship - type of ship, country, era, etc.
One clue may be the ''17 - '' in the lower left on the front side. There are sailors crowded on the left side, and a few others in other parts of the ship. The flag on the far right looks like the US flag
As two thirds of these cards are preWWI, and the others are mostly pre WWII, is this a WWI battleship?