Current stable version is: 1.7.0 (26/11/2013).
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CHANGELOG:
Version 1.7.0:

FIXED: Some minor bugs and translations.

NOTE: Caesium automatic updater has some problem (related to the host) and you need to manually download the newest version.
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Version 1.6.1:

FIXED: Hotfix for some bug in 1.6.0
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Version 1.6.0:

FIXED: Caesium compresses up to 200% faster
Profile files not storing all the new info
Compression slider value
Crash previewing some images
Some iussues with resolution changes

ADDED: Caesium will always now prompt to exit if there's at least one item

NOTE: Caesium now uses Qt5, which means its performaces are improved significantly
at the expense of an increase in size.
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Version 1.5.0:

FIXED: Program won't freeze while previewing many files at once.
Windows 8 ugly style. 
Caesium won't delete the original files if it has already skipped them.
Some freeze while loading previews.

ADDED: Change resolution while compressing.
Windows 8 support.
Styles.
Possibility of keeping data and layout after closing the program.
Possibility of don't delete original file if input and output format are different.
Minimize to tray option.
Automatic Preview.
Possibility to keep the file type while compressing.
Now Caesium can keep the folder structure.
Some other minor features.
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Version 1.4.1:

FIXED: Language when opening a Lis/Profile file.
Portable and Source Directory names. 
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Version 1.4.0:

FIXED: List usage.
Settings file.
Modal windows.

ADDED: Caesium profiles.
File association in the installer.
You can choose the toolbar icon size now.
Ask before exit option.
Scan subfolders when opening a directory.
Changelog on the updater. 
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Version 1.3.1:

FIXED: Taiwanese flag.
Updater bug.
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Version 1.3.0:

FIXED: Crash occurring when a file in list doesn't exists.
Multiple selection in the list (by dragging the mouse) are now working.
Some new icon.
New (more colorful) settings window. 

ADDED: Traditional Chinese translation (thanks to Zkm).
Right-click menu on the list.
Caesium now can delete the file from list AND Hard Drive.
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Version 1.2.0:

FIXED: Minor bugs.

ADDED: German translation (thanks to Markus).
New internal updater.
Caesium now can delete the original files after compressing.
Last Modified and Creation Data can be kept in the compressed file.
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Version 1.1.0:

FIXED: Gray glitches on Explorer preview after compressing images.
Rename bug on PNG files.
Multilanguage system improved.

ADDED: Japanese and French language (thanks to Tilt and Dodich).
Now Caesium will try to load the system language as default at the first start.
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Version 1.0.0:

FIXED: Memory usage.
No more crashes while compressing a large number of pictures.
Complete recoding.
Overwriting bug.
Renewed graphic.
New about dialog.
Some other bug. 

ADDED: Zoom in preview.
Multilanguage support.*
EXIF metatag support. 
Additional settings.
Some mini (but useful) stuff. 

*Caesium needs translators. If interested, contact me.
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Version 0.5.0:

FIXED: Thread usage while compressing. Now the process won't freeze anymore, and shows realtime informations.
Compress icon. 

ADDED:Progress percentage and which file is current under process.
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Version 0.4.0:

FIXED: When starting from Start Menu, the "Remember Last Dir" option were not work. Now it does.

ADDED: Save & Load list option.
Now the application checks automatically for updates at startup. 
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Version 0.3.0:

FIXED: Minor bugs.

ADDED: New style. Icons by PC.DE.
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Version 0.2.3:

FIXED: Invalid suffix crash: previously some special character causes a program crash.

ADDED: Remember the last used directory: on exit, you can choose to remember the last directory you used for saving compressed pictures.
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Version 0.2.2:

FIXED: "Fixed window option": the option now works properly.
The Format combo box can't be edited now.

ADDED: Nothing :0
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Version 0.2.1:

FIXED: The main window can be minimized now.

ADDED: Message at the end of the compression.
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Version 0.2.0:

FIXED: Antivirus issues: some antivirus recognise the installer as infected.

ADDED: Portable version of the software.