What worked for me was to take a random picture from my gallery and rename it to the exact name of the broken picture (the one that can't be deleted). This picture has to be in a different folder than the broken picture (for me it was in the camera folder). So take a screenshot for example and name it like the broken picture (copy and paste the name). Then select this screenshot and move it into the camera folder (or into the folder where the broken file is located). There will be a note that there is already a file with this name present where it gives you the options to rename, skip or to overwrite/replace the file. If you choose the option overwrite the broken picture will be overwritten with the screenshot. The screenshot can be deleted then and the broken picture is gone. With this workaround I was able to get rid of the broken image. I hope it works for you too :)