Put both pictures in the report using the insert picture function and suppress each one by right clicking, format picture, click the suppress box.
Picture 1 click the suppress box and in the formula type
{SP.fieldA}<>'X'
Picture two click the suppress box and in the formula type
{SP.fieldA}='X'
You can even put them on top of each other because only one will be showing at a time. I do this often with text boxes and data fields.