Prioritizing a Task in high concurrent image processing (prevent stacking)

Question

Is there an option in C# to give a priority for Tasks that ran first. I am using a code for image processing. In my testing and in high workload (e.g. 100 concurrent parallel image processing and uploading), when I run the tasks in parallel without any waiting (e.g. Thread.sleep(1000), the upload stacks up and the almost all the images are sent after most of the images have been uploaded.

I want to give priority to images that enter first to get out as fast as possible. In high load I see that I need to wait a long time until I see the first image getting out.