Not entirely sure where you want to delete the pictures from ..
If you mean the blog site, it's probably best to ask the admins on there.
If you mean you're seeing blog pictures in your phone gallery, then you could try clearing the browser (or whatever app you're using for the blog) cache. Alternatively, get a file manager from the Play Store (I use a free one called File Manager) and try clearing the Downloads directory. If the images aren't there, use the Search function to find and delete them.
