Do not use spaces in names of your files including images.
Images uploaded via “Insert” are only available in that page.
As of now: google puts image in the same folder as your page, and because every page in google has it’s own directory/folder – it’s hidden from other pages. So, you will have to upload it to each page taking up space on the server. Deleting page will delete images associated with that page.
Save space: If you need to use the same image on multiple pages without uploading it to each page here is workaround:
Upload to the first page and write down the url of that first page, in my case it is page images, so url for it is http://sites.google.com/site/oksanazsite/images/
The file name of the picture I uploaded is apple_tree.jpg, I add this picture name at the end of above directory http://sites.google.com/site/oksanazsite/images/apple_tree.jpg and now I have direct link to that image. So, when I go to upload this image to a different page, I choose Web address (url) and paste it there. If you ever to delete that first page, then image will be deleted also, and your image links on other pages become broken. You need to remember to recreate image insert on those pages.
below is image (more like a space for the image) that was uploaded to a different page, then that page was deleted.
gif animation will not work in google sites text editor. It will just show the first frame. To get it to work you have to click on the image and it will open in it's own page - image1
To go around it: If you host the image somewhere else and use url option when inserting image - it will display properly -image2 (in my case I uploaded it to google documents and using direct link to the image file)
image1
image2
This below is insert of google document containing my gif image.
Note: the link to the google document is different than direct link to the image file used in this document.