On modern PCs, a file doesn't actually go away when you hit the Delete key. The bits on your storage drive that represent that file simply get flipped to a hidden state, and they're tagged to be written over by other bits later. This requires less time and processing power than scrubbing every deleted file off your hard drive. Gradually, bits from other files overlap the old file and eliminate it. This process could take seconds or weeks, depending on how much you use your drive and what kinds of files you're putting on it.
On a home desktop, overwriting files to delete them usually isn't a problem. But with a laptop or tablet that could more easily get lost, damaged, or stolen, you may want to kill files completely, so no one can rummage through your trash and find personal information. Here are two options for full shredding.
Fully deleting with Free File Shredder
While Windows doesn't have a built-in utility to truly delete a file, there are several free third-party tools. One is appropriately called Free File Shredder. When you open this app, it asks if you want to delete a file, a folder, or the entire contents of your Recycle Bin. To delete a file, click Next and drag-and-drop your file to the Shredder window. To delete a folder, click that radio button, Next, and Select to navigate to the folder you want to shred.
You can choose three types of shredding. Quick Delete should be enough for most people. It replaces the file's bits with mostly randomized bits generated by the app, and you can tell Free File Shredder to do that up to 999 times. This method should take less than the blink of an eye to shred an image or a document.
Fully deleting with Recuva
Recuva is made by Piriform, the same people who make CCleaner, a popular tool for clearing junk data off your PC. Although Recuva is designed for recovering files that you've accidentally deleted, it can be used to make them un-undeletable as well. When you open the app, click the Next button, Next again to choose All Files (the default option), the radio button next to In the Recycle Bin, and Next one more time. Click the Start button to begin scanning. The process should take a few seconds, unless you have gigabytes of stuff in the bin.
Click the Switch to Advanced Mode button, Options, the Advanced tab, and the drop-down menu at the bottom, and choose how many times you want the files to be securely overwritten. Your choices are 1, 3, 7, and 35. Click the OK button to save your changes. This will return you to the previous window. Check the top-most box to select all files in the Recycle Bin, right-click any files in the list, and click Secure Overwrite Checked. Click Yes to confirm and Yes again when warned about SSD devices. Using the seven-step overwrite option, about 5GB worth of files took less than 30 seconds on our system. The speed of this operation will vary according to how fast your hard drive and CPU are.