You can upload photos or graphics files into your WordPress blog.
Make sure use one of these image types: .jpg/.jpeg / .gif / .png
to a post or page on your WordPress blog.
Most images from the camera saved your computer either jpg or tiff file. Some DSLR has raw or dmg files too, which they are usually very big size images.
If you do not want to put large image on your blog, you can use thumbnail option.
Upload Images from Your Computer
When you are uploading image to a WordPress site, the default large size is 1024. That is pretty big if you like to view a photo on the web.
However if you are uploading a photo from your camera, there is a good chance WordPress blog will give you error message. It will not upload the image, unless you change the size of the image or your media setting.
I would recommend to make 950 size images for your blog before uploading them. This can speed up your blog page and you do not have to fill your hosting package with lots of large image files. If you use too many large images on the blog, your website will be slow down quite a bit. So you have option to make large images clickable with either thumbnail or small sizes as well as you can re-size all your images before uploading to your site.
Free Softwares for PC Windows Users:
If you are PC user Irfanview freeware does great job creating thumbnails, resizing as well as a few simple photo effects.
Learn more about this freeware here: http://www.irfanview.com
Picasa is an image organizer and image viewer for organizing and editing digital photos, plus an integrated photo-sharing website.
It works on PC and MAC. Learn more about it here: http://picasa.google.com/
Free Picture Resize Starter
You can resize images and optimize them for particular purposes. You can resize multiple files, creating slide shows and icons too.
Learn more about this freeware here: http://download.cnet.com
Free Apps for Mac Users:
Create perfect thumbnails
This app makes it easy to crop out a small thumbnail from a larger image.
Learn more about this free app here: http://opcoders.com/thumbnailcutter
Not free apps, but worth to buy:
Photographers and webmasters often find themselves spending too much time converting, resizing and watermarking (with copyright, for example) images. EasyBatchPhoto frees you from these repetitive tasks by processing hundreds, or even thousands, of images with a single drag-and-drop.
Learn more about this free app here: http://yellowmug.com/easybatchphoto/
Xee is a lightweight, fast and convenient image viewer and browser. Display a large number of image formats. Effortlessly copy, move, rename and delete of images while viewing. Learn more about this app here: http://wakaba.c3.cx/s/apps/xee
PicFrame helps you combine multiple photos into amazing looking frames that you can save to your computer or share to Facebook. With 67 adjustable frames, support for up to 9 photos in a single frame, rounded corners and plenty of border patterns, you will always have a unique look.
Learn more about this app here: http://activedevelopment.co.nz/picframe-for-mac/
A photo collage in minutes. Tailor each individual image using an image filter (black & white, sepia, sharpening etc.) to your needs. Easily change the size of any document or predefined template. Crop any image to your liking.
Learn more about this app here: http://zykloid.com/posterino