I'd like to prevent direct image viewing without the entire page.
If someone goes to
mysite.com/images/image1.jpg forward to mysite.com/image1.htm
mysite.com/images/image2.jpg forward to mysite.com/image1.htm
mysite.com/images/image3.jpg forward to mysite.com/image2.htm
mysite.com/images/image4.jpg forward to mysite.com/image2.htm
Is Htaccess the best way to do this and how would I set it up?
You can check for the "Referer" request header. Browsers sometimes use it to tell the server what URL told the browser to load the file. However, not all browsers will use the referer header and it can easily be forged, so this is not a sure way to prevent direct linking to your images.
You can add this at the top of your htaccesss file:
RewriteEngine On
RewriteCond %{HTTP_REFERER} !^https?://mysite\.com/
RewriteRule ^images/(.+)\.jpg$ /$1.html [L,R]
Reading the comments, I'd recommend to avoid maintaining N RewriteRules for N images. Such a setup will turn into a maintenance nightmare for the site admin who will need to copy and paste a new rule for every new image on the site. And if you ever need to change the rules, well... good luck with that.
If you have the flexibility to choose a better directory structure, it can simplify your .htaccess file down to a single rewrite rule. In that case, you can choose a directory structure where given a path to an image you can easily determine the path to the page it belongs to. For example:
root/
.htaccess
page1/
index.html
image/
image1.jpg
image2.jpg
page2/
index.html
image/
img.jpg
Here the rewrite definition within root/.htaccess is simple (adapted from @jon-lin's answer):
# Rewrite any image URL `/<page>/images/*` to `/<page>/`.
RewriteEngine On
RewriteCond %{HTTP_REFERER} !^https?://mysite\.com/
RewriteRule ^([^/]+)/image/ /$1/ [L,R]
RewriteRule to rule them all./<page>/image/.