fixes for docs images

Author: tmcgrath325

docs/src/assets/picture_2.png renamed to docs/src/assets/Picture.png

@@ -7,7 +7,7 @@ CurrentModule = CounterMarking
 [CounterMarking](https://github.com/HolyLab/CounterMarking.jl) analyzes experiments on [scent-marking in mice](https://www.sciencedirect.com/science/article/pii/S0003347287800167),
 specifically images of urine countermarking visualized by the [ninhydrin reaction](https://pubs.acs.org/doi/full/10.1021/jf030490p):
 
-![A ninhydrin-stained image](assets/picture_2.png)
+![A ninhydrin-stained image](assets/Picture.png)
 
 The yellow spot corresponds to a stimulus provided by the experimenter, and the small light-blue spots are deposited marks.
 

docs/src/assets/averaged_calibration.bmp

@@ -24,7 +24,7 @@ function gui(
         btnclick = Condition(),         # used for testing
         whichbutton = Ref{Symbol}(),    # used for testing
         preclick::Union{Int,Nothing} = nothing,  # used for testing
-        background_path = nothing,  # used to correct for non-uniform illumination (see joinpath(pkgdir(@__MODULE__),"docs","src","assets","blurred_calibration.bmp"))
+        background_path = nothing,  # used to correct for non-uniform illumination (see joinpath(pkgdir(@__MODULE__),"docs","src","assets","blurred_calibration.png"))
         crop_top::Int = 0,          # crop this many pixels off of each side
         crop_bottom::Int = 0,
         crop_left::Int = 0,