Flickr provides free accounts for up to 1,000 images. If you would like to upload more than 1,000 images, you can create a Flickr Pro account. To create a free Flickr Pro account, fill out this Flickr NonProfit Account Request form. You should receive your Flickr Pro account within one week of submitting the form.
When filling out the form, under Organization Name, enter your TEDx event name (e.g. TEDxVienna). In the field labeled Tax ID Number, enter the URL of your official TEDx event page found on TED.com (e.g. https://www.ted.com/tedx/events/27458). If you need any help with this process, you can contact Flickr support.