When you post a blog entry, you typically include a full-sized photo of the item or person being discussed. However, if you have a shorter article or if the photo is too large to fit on one page, you may include a thumbnail of the photo instead.
Thumbnails are just small versions of photos that are displayed when someone scrolls down your blog post. They’re useful for quickly identifying the photo and for saving people from having to scroll all the way to the bottom of your post to see it.
When people click on a thumbnail, it takes them to the full-sized version of the photo. Thumbnail sizes can vary, but most blogs use 300×250 pixel dimensions.
This means that a thumbnail will be about one-sixteenth of the size of a full-sized photo.
Keep in mind that including thumbnails in your blog posts can take up some valuable space on your site. If you have limited space, think about whether or not thumbnails are really necessary and whether they’d make people more likely to click through to your full-sized photos.