I have started a news website for a specific area of business one year ago. The website lists news and for every post there is a featured image. Unfortunately, there have been posted about 1500 news in a year and the website is taking 1,07Gbytes of space. This seemed totally insane to me as joomla is had been only some Mbytes and there were no big additions from my side (like files or graphics etc.).
I did a HUGE mistake. I trusted the joomlaworks guys and installed K2. The main reason I did this was that the default joomla article manager did not offer to save a featured image for each post. But this was added in the new 3.0 version !
K2 does something extremely foolish. If you save a photo of 2 Mbytes, then it will save the original and 4 additional ones, one for each size (Small, Large, Medium, XL). Insanely, you upload a 2Mb image and it ends occupying 4Mbytes of space !
The hosting provider gives me 2Gbytes of space to store my files. I have started to lose my sleep at night because the space expands day by day and If gone beyond 2Gbytes, I will have to upgrade the hosting plan and I do not have the money to do this.
I believe I have three choices:
Move all items, categories, images from K2 back to Joomla articles that is much faster and then upgrade to version 3.0 which supports featured images. This seems extremely difficult and I do not know If it's possible at all. Even If I move all table rows from K2 to Joomla, I don't feel comfortable with 1500 ones and the images' paths are not saved in the db. Chaos.
Move everything to wordpress. No idea how to do that at all.
Compress the images that are in cache or search for ways to stop K2 doing that.
k2 saves the images in two different folders. One folder holds exclusively the originals, and the other folder holds all the resized versions. Technically you can just delete the folder with the originals because those are not the ones used in the articles or anywhere else on the website. Let's not speak poorly of k2 because they save the originals. I think it's a good feature. I once needed to go into that folder on my host and find a file that was deleted from my computer. Also you could easily in the future use that folder to rebuild all the resized files in case you want to change the sizing in layout.
I would just back up the folder every once in a while and delete the copy on your host. That should save a lot of space. Also you can set an option that the resized files are lowered in quality so they don't take up so much space. There is an option in the back-end. At 70-80% the photo quality is still great.