What needs to be understood is that the attachment feauture places the image files onto Dave's server. This means that not only does the server have to have sufficient space to store it, but when the server is backed up, those files contribute to the total amount being backed up.
So, no, this thread alone is not causing a problem, but it is contributing to the volume of what is stored on the server, perhaps to an unneccessary extent.
My advice to all who enjoy attaching pictures is as follows:
1. As Padraic mentioned, reduce the picture size as much as possible before uploading;
2. Better yet, find a hosting service to host your pictures and then use the image tool to imbed the image into your post.
I occasionally use the upload feature when I need to post a pic from my hard drive and cannot host it elsewhere, such as when I am at a computer where uploading is not allowed, but I try to limit the size and the occasions I do so for the reasons cited.