This is my first ever postcard sent from Chad! Sadly, it came with (quite) clear cancellation, but without any stamps. There are no signs on postcard that there was a stamp at all! I removed Chad from my list of missing countries, but I hope that I'll receive at least one more postcard sent from there, but with stamp on it.
Anyway, the postcard I received shows the rocks painted by Jean Verame in 1989. Those several cliff formations are colored in bright white, blue, violet, black and red colors. These cliffs differ from the common brown - red colours of sandstone formations and create eerie feel. They're located in the northern part of the country, near Bardai, Tibesti Region. source
Thank you Hamid!