It looks like you've got a problem with the shutter. Possibly one of the "blades" in the second curtain is missing and allowing light to strike the sensor between the time after the second curtain has completed its travel and the time the sensor is read out.

Here's what a 70D shutter curtain looks like. Does the shape of the 2nd of four individual blade that make up each of the curtains look familiar to you?

It is fairly easy to confirm. Just set your camera for manual exposure with a fairly long shutter time. Say 1 or 2 seconds. Enable mirror lockup. Remove the lens, point the camera so that you can see into the front of the mirrorbox, and press the shutter button all of the way down. This will raise the mirror while leaving the shutter closed. The first curtain should be entirely covering the sensor. If there's a gap anywhere that lets you see part of the sensor at this point then the first curtain is faulty. Press the shutter button again to expose the sensor. After the first shutter curtain opens, watch carefully as the second curtain closes 1 or 2 seconds later. If there's a problem with the second curtain you should be able to see it before the mirror drops down and the shutter resets. Don't blink, though, or you'll miss it!

To see the second curtain longer you can go to Live View and select Silent LV shooting mode 2 (see below). When you press the shutter button all of the way down hold it down and you should be able to see the second curtain completely covering the sensor. If there's a gap anywhere that lets you see part of the sensor at this point then the second curtain is faulty.

As far as having it repaired goes, it doesn't really matter. A shutter replacement will include both a new first and second curtain in the shutter assembly.

If it is only one of the curtains that is the problem there may be a workaround that will allow you to take images, albeit with greatly reduced functionality. You'll have to shoot using Live View from one of the Creative Zone exposure modes (P, TV, Av, M, or Bulb) and you'll give up the possibility of using any flash, even a non-Canon manual flash that doesn't communicate at all with the camera.

Please note that the following is how my Canon 5D Mark II (2008), 7D (2009), and 5D Mark III (2012) operate. The 70D was released in 2013. My 7D Mark II (2014) operates slightly differently.

From within the Live View menu (the last red menu tab), select Silent LV shooting, press the Set button, select Mode 1 to avoid using the second shutter curtain or Mode 2 to avoid using the first shutter curtain, then press Set again. It's covered on page 231 of the EOS 70D Instruction Manual.

Notice the note at the bottom of that page: If you have a flash connected to the hot shoe that can be detected by the camera (generally any E-TTL capable flash or flash trigger that is turned on), the Silent LV shooting setting will be disabled. If you have a manual only flash connected to the hot shoe the hot shoe is disabled in Silent LV shooting and will not fire the flash.

If the 70D operates like the newer 7D Mark II, the second curtain closes to end the exposure in both mode 1 and mode 2 of Silent LV shooting and the above workaround will only work if the first curtain is the faulty one.

For more about how the Silent LV shooting modes work and the difference it makes to the shutter curtain sequence, please see this answer to: What's the difference between Canon's silent and non-silent shooting? Although that question is regarding the EOS 5D Mark III, the Live View silent shooting modes function similarly with the 70D (with the possible exception to which curtain is used in Silent LV shooting mode 1 as mentioned above).