You can add as many pictures as you like to your board.
There is a limit of 50 videos that each Boards user can upload to the platform. It's important to note that if you upload videos to your board and then delete them, the video count on your account will not decrease. This is because the limit is based on the total number of videos you have uploaded to your account, not the number of videos currently visible on your board.
However, there is no limit to the number of YouTube or Vimeo videos you can add.