Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an m x n picture consisting of black 'B' and white 'W' pixels and an integer target, return the number of black lonely pixels.
A black lonely pixel is a character 'B' that located at a specific position (r, c) where:

Row r and column c both contain exactly target black pixels.
For all rows that have a black pixel at column c, they should be exactly the same as row r.

 
Please complete the following python code precisely:
```python
class Solution:
    def findBlackPixel(self, picture: List[List[str]], target: int) -> int:
```