I want to darken an image - how should I do that?

If you are intending to make the whole image a little darker, click on the Look Up Table (LUT) button.  This tool shifts the grey scale of the entire image, making all elements a bit darker or a bit lighter.  To do this, click and drag the middle dot on the diagonal line toward the lower right corner.  The more you move that dot, the darker you make the image.   You can undo the change by clicking on the Undo button on the same tool, click on the Undo button and the Metron tool bar, or click on one of the Filter buttons (1,2,3,4).

Can I use the Window Leveling button to darken an image?

You can use this button tool to darken an image but that is best done with the Look Up Table button.  The Window Leveling tool originates from human medicine with Radiologists using this dynamic tool to help them increase the visibility of specific anatomy of interest.  If you click and hold down the left mouse button while then moving the mouse around in all directions, you will change the visibility of image elements - accentuating some diminishing others. It is more of a selective darkening and lightening method.  

Is the patient birthday important? 

Though not required, it is a good habit to add the patient birthday to the Metron patient record.  The birthday does affect image acquisition or image processing. Metron's equine podiatry measurement analysis has the option to present score details based in part on equine patient age. For those practices that may send X-Ray studies to others by DICOM for review, the accompanying DICOM data will include the patient birthday.  Any veterinary radiologist will want to know the patient birthday as part of their overall patient/case study.