Here is an overview of some old postage stamps from the period from 1875 to 1919, depicting, among others, the heads of state Frederick VIII and Christian X:

1. **Denmark**:
   - **Frederick VIII**: Frederick VIII was king of Denmark from 1906 to 1912. His image appeared on several Danish postage stamps during his reign.
   - **Christian

2. **Norway**:
   - **Oscar II**: Oscar II was King of Sweden and Norway from 1872 to 1905. His portrait was featured on Norwegian postage stamps of that period, as Norway was united in a personal union with Sweden until 1905.

3. **Sweden**:
   - **Oscar II**: In addition to Norwegian postage stamps, the portrait of Oscar II also appeared on Swedish postage stamps during his reign.

This is a brief overview of some stamps with heads of state from that period. There may be other stamps with other heads of state from other countries that were issued in the period mentioned.