Viewer

Replaces the browser's default image resizer to a more customizable version. For instance, it's possible to set the initial sizing mode or disable the resizing totally, it can detect if an image has higher resolution, adds possibility for rotation, options for changing background color or image border, zooming to a selected area or zooming with mouse wheel, and more...

Hover zoom

Enlarges thumbnails and linked images (or even linked thumbnails) into a popup with just a mouse hover.
As well as the Viewer, it's also fairly customizable with some extra features, such as full-zoom which allows you to view the image with original size in the same tab, rotation or it can load image albums as well.

Tools

This section contains global features or features that have less options.

• Shortcuts - they can be used both on Viewer and Hover zoom
  
• Opening images - many ways for opening images from web pages (e.g., background images)
  
• Send image to... - it sends the image address to an online service (e.g., reverse image search, image editor, gif frame extractor...)
  New service can be added in preferences (one per line).
  Format: "[+]Name|search engine's URL". In the service URL is placed the image address with the %url variable.
  Example: TinEye|http://www.tineye.com/search?url=%url
  If you put a "+" sign before the name (e.g., "+TinEye"), then it means that the service will be used when the shortcut is used. Multiple entries can be enabled, then all of them will be opened.

Sieve

This is a set of rules which are helping the extension to find the larger images.
The rules are based on regular expressions, JavaScript and a bit of HTML.

Gallery

This is something like a bookmark for images. It stores only the image address with a thumbnail, and if possible, then one or two source link. The "Source", which is the address of the page where you've seen the image, and the "Target", which is the address of the link (if it wasn't the same as the zoomed image address).
When an image is opened or "hoverzoomed", then pressing the shortcut (G by default) will add it to the list without any questions. Shift + G will prompt for labels. Deleting images from the list: Ctrl + Right click on the thumbnail cell or Ctrl + Click to select some and the minus button from the button-list. Shift + Right click on a cell to edit the labels.

Grants

At Grants you can tell on which sites can the extension work.
It's also possible to block just some Sieve rules.

Syntax: grant operator (optionally followed by rules separated with commas) colon address
(!|!!|~|~~)[rule1,rule2,...]:(*|string|regular expression)
Also there is possibility to add comment lines, simply by starting the line with a ; (semicolon).
When you double the grant operator (! or ~), then it means that you want use regular expression in the URL. "*" means everything.
Example for blocking on all sites:

!:*

Blocking all sites except opera.com (actually it will allow any URL that contains the "opera.com" string, and yes, the order matters):

!:*
~:opera.com

To block a few sites:

!:http://www.google.com
!:opera.com
!!:^ftp://

Blocking on all Google sites, except German and French:

!:http://www.google.com/
~~:^http://www\.google\.(?:de|fr)

Allowing only the "MyOpera" and "LinkedImages" rules here on my.opera.com:

~#MyOpera,LinkedImages:my.opera.com

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For the extension's icon thanks goes to http://esk6a.deviantart.com/

Known issues

# (vw) sometimes after moving the selection (freeZoom) on an image, the rectangle will lose its position
# (vw) Rotated image has incorrect position
# (hz) Rotated image position is not always correct when using full-space
# (hz) SVGs sometimes are not displayed at first time (maybe an Opera bug)

v0.9.1 - April 10, 2012

You can read the changes at the Archive.

Install v0.9.1

v0.9.1
This update mostly fixes the bugs from v0.9, and includes Finnish (by Opeeera) and Polish (by pafflick) translations.

Probably some of you are using DuckDuckGo, and noticed that it doesn't work when Imagus is enabled. What causing the problem is needed for a feature (frame detection), so I can't just "fix" it, but as a solution you can block the extension on that site. Add this to Grants:

!!:^https?://(?:www\.)?duckduckgo\.com/

Or I included a hidden rule as a comment too, so if you go to Grants and set the textarea to its default value (Ctrl+Right click), then two rules will appear (the other one is for youtube and vimeo, read below...). Remove the semicolon from the beginning of the line that is containing "duckduckgo" and Save.

v0.9
The changelog won't tell you:

• Most important thing is that you MUST update the Sieve after install, because the old one isn't compatible with this version. The extension won't do it by itself, so if you have made some rules, you will be able to export them first (at least I think it'll work, but I haven't tested). I'm not sure yet, but probably there will be one time when you have to do this.
• There are some tips (hopefully understandable enough) at the Preferences page for specific options, but right now only in Viewer.
• Besides Hungarian, now the extension has Russian translation too (thanks to Rodny).
• The loader changed to an animation, and instead of messages it will have different background colors. Colors: white - Loading, lime - Resolving, yellow - Failed, orange - Error.
  Probably the last two will be dropped later, instead of them the loader will just disappear, because at the moment if you don't know what the colors are, it may be a little misleading, since the animation won't stop, just the background color will change.
• Shift + right click on an image will put the image into a popup. The purpose of this tool is to make available the functions that can be used on the image when it's in the popup (e.g., rotating, sizing or saving it to the gallery).
• Enabling full-space (which is enabled by default) in Hover zoom allows the image to use all available space, so the image can go under the cursor. Similar to the "Placement: center" option, but in this case the image will still follow the mouse cursor. It has a shortcut (F) to temporarily switch to normal mode (or back). It doesn't work on SVGs.
• I mentioned earlier that Imagus is able to play linked YouTube videos in the popup. If someone interested, I included a rule which will work for YouTube and Vimeo videos. First you need to enable the rule called "yt-vimeo_video" under Preferences / Sieve. Probably you don't want it to work on the main sites, so just add this line to the Grants:
  !!yt-vimeo_video:^https?://(?:vimeo|www\.youtube)\.com/
• Image pile is for viewing multiple images in one popup, or in other words; support for image albums. When you run into an album in the caption two numbers will appear (even if you disabled captions). The second number indicates how many image is in the pile, the first is the index of the current image. Moving between images: space, right arrow, page down - move forward, shift+space, left arrow, page up - move backward, up or down - 5 step forward or backward, home or end - move to first or to end, shift+end - manually enter the index.
  After install, here are some examples for imgur albums, and for imageshack, or just visit photos section here at MyOpera for other examples.
• And finally the image lister... It can be invoked by pressing Alt+Shift+full-zoom key (which is Z by default) (it is basically a combination of full-zoom and image pile with the image thumbnails).
  If the popup is visible and you press the shortcut, then it will list the images from the popup, which can be only one image or a pile. If the popup is not visible, then it tries to collect images from the current web-page.
  At top left you'll see a rounded white square, and if you move your cursor over it, the list will drop down. Everything works same as in full-zoom, all shortcuts are available here too. When the cursor is above the list, it's possible to slide it with mouse wheel.

The rest in the changelog is less important or it's straightforward enough (I hope).