How to fix uneven formatting of image captions

I have many images on a website. Some have captions that show as a line of text below the image; other images use a grey gradient over the image with the caption. I want all the captions to be handled the same way, with the text below the image (it is so much easier to read than grey text on a grey gradient). The second row of images on https://www.susanlittle.com/miniature-original-watercolour-paintings/ show the problem captions (using the gradient over the image). The first two painting images on https://www.susanlittle.com/gallery-watercolour/ show the ideal handling of captions. How to I make all captions formatted in the same way? Thank you.