MediaLab doesn't recognize pictures

Hello all,
I've been trying to put some pictures on the media lab for participants to rate. However, media lab could not recognize the pictures.
Instead, media lab shows the link of the picture, which is identical to the link of the picture in the computer.
I have no idea why media lab shows some of the pictures, but not all of them.

All the images are of a fixed pixel size and resolution, and they are all in the .bmp format.
Does it matter that I converted the images from JPEG files on a Macintosh computer?
Are there any ways I can convert images so they are universal to the roots so Media Lab would be able to recognize it?