Picuter problem

We have developed a project, we didn't have any problem till now, but now we have a strange problem!
All the picture related to Sitefinity dont appear, either in frontend or backend!
can anybody help me?!

We ran in to this when we upgraded to 1501 at some point, and our .Net mode on our shared host was NOT set to Integrated Pipeline. We changed it and it's been working ever since.