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, return the number of black lonely pixels.
A black lonely pixel is a character 'B' that located at a specific position where the same row and same column don't have any other black pixels.
 
Please complete the following python code precisely:
```python
class Solution:
    def findLonelyPixel(self, picture: List[List[str]]) -> int:
```