@jp_grennier: For individual image like http://jpgrennier.com/artwork/, I see that you have one image align left and another right with paragraph code. That is why it is not working properly. Image in paragraph with align left is supported to be with text paragraph. In a paragraph, you can only have one image. Try adding in the full image or large image with center align.
About your Gallery page http://jpgrennier.com/writing/, I see that you have added 2 column layout gallery. For which your image is small. Change the thumbnail image size from “Settings => Media”. Then after you change the size, you need to regenerate the images for old images, as you just changed the size. To do that you need to install plugin “Regenerate Thumbnail” and regenerate the image. This will make your image big as per you need in the layout. You current image size is only suitable for 4 column gallery.
There is another cool way to create Gallery. If you see the example at http://catchthemes.com/demo/catch-everest/gallery/. This is just a normal gallery after installing “Jetpack” plugin and activating Carousel and Tiled Galleries module of Jetpack plugin.
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