Hello 
Just a nice tip I learnt today on an apple related website, but could be applicable on windows too if you find the equivalent software !
BEWARE there is a loss of quality, although difficult to notice, in the process. Just so you know. in my case I don't really care, but it is nice to know.
1/Download and install for free this app : http://imageoptim.com/
2/Open the finder and search for "jpg" on your root folder (save your computer HD before, that's recommended, just in case. I have had no problem, but again, be careful)(unless you wanna select which folders you do care about in terms of hi-fidelity). The finder window should now list all your jpg files
3/BEWARE once this is done, the process starts and the original files are overwritten : Drag into the ImageOptim window. It uses a lof of your CPU power and therefore makes it get real hot. If your computer has a poor cooling system you might think about it twice. On MacOsx I monitor my CPU temp with smcFanControl
4/Wait. Profit.
Optionnal : do the same with .png files. I have had a 30% save on average on png files, and just a bit less than 15% on jpg. Since I shoot actual photography photos with raw format, I don't care about the tiny loss in my jpg which are downgraded exports anyway. The other jpg, i.e. funny or old crap pictures, I do not care about. Note that at least in my case png were longer to process. Even though they are not heavy, iPhoto preview pictures can be compressed to up to 80% easily, and the result is almost the same !
Again, I am not responsible if you do a mistake especially if you choose the root folder.
If someone knows of a similar software that can work on videos, one after another, like this one, even for a very tiny loss (of a few %), I would be interested. At least on .mp4 videos since they seem to be easy to control in terms of codec !

Just a nice tip I learnt today on an apple related website, but could be applicable on windows too if you find the equivalent software !
BEWARE there is a loss of quality, although difficult to notice, in the process. Just so you know. in my case I don't really care, but it is nice to know.
1/Download and install for free this app : http://imageoptim.com/
2/Open the finder and search for "jpg" on your root folder (save your computer HD before, that's recommended, just in case. I have had no problem, but again, be careful)(unless you wanna select which folders you do care about in terms of hi-fidelity). The finder window should now list all your jpg files
3/BEWARE once this is done, the process starts and the original files are overwritten : Drag into the ImageOptim window. It uses a lof of your CPU power and therefore makes it get real hot. If your computer has a poor cooling system you might think about it twice. On MacOsx I monitor my CPU temp with smcFanControl
4/Wait. Profit.
Optionnal : do the same with .png files. I have had a 30% save on average on png files, and just a bit less than 15% on jpg. Since I shoot actual photography photos with raw format, I don't care about the tiny loss in my jpg which are downgraded exports anyway. The other jpg, i.e. funny or old crap pictures, I do not care about. Note that at least in my case png were longer to process. Even though they are not heavy, iPhoto preview pictures can be compressed to up to 80% easily, and the result is almost the same !
Again, I am not responsible if you do a mistake especially if you choose the root folder.
If someone knows of a similar software that can work on videos, one after another, like this one, even for a very tiny loss (of a few %), I would be interested. At least on .mp4 videos since they seem to be easy to control in terms of codec !