Lower load time???

My suggestion : resize and recompress the files you’re putting up on your blog. Unless your purpose is precisely to share high resolution pictures, you’re annoying your visitors with pictures taking so long to lad.

If you’re after a freeware for resizing in batch, I’d suggest Xnview : open the folder with the pictures, select the ones you want recompressed, right click, chose “convert”, it will open a window in which there’s a “transformations” tab, and among the list of the transformations there is “resize”.
Usually, a vertical size of 1000px is usually considered as very good on the internet, for instance.
Edit : don’t overwrite your originals, specify to Xnview a different output folder, or have them be created in a separate subfolder !