Putting my painting in my homemade light diffuser helped somewhat but I still had glare speckles. I found a nice way to save those speckled photos tho. Here's how I did it in photoshop:
Under FILTER go to NOISE > DUST AND SCRATCHES. By setting the Radius at 1 or 2 and the Threshold between 15 and 25 I was able to make the speckles disappear. Be sure to zoom in and make sure you aren't losing any brush detail tho. The number I used may be different for different resolution photos also.
Some tips on adjusting photos:
After cropping my painting in photoshop I start with the overall values. The first step is checking the levels:
IMAGE > ADJUSTMENTS > LEVELS
I usually move the black arrow in to the right just to the point where histogram levels start to climb, I do this with the white arrow on the right side also. This cleans up any haziness and gives you nicer contrast. Then on the midrange arrow I try to match the values of my actual painting moving it to the right or left:
Next I work on color. I mostly use this tool to make color adjustments:
IMAGE > ADJUSTMENTS > COLOR BALANCE
If the colors in your photo just don't seem to match the intensity of your actual painting try using this:
IMAGE > ADJUSTMENTS > HUE AND SATURATION
Try boosting the saturation a bit to match your painting.
There are probably 10 different way to achieve the same results in Photoshop, so here's my method to add to the pile!