When opening the attached file (pouch.gif, 3 MB), eog uses 1.2 GB of ram. Google Chrome, by contrast, uses 100 MB (including plugins and a tab or two).

I think the reason may be that it contains 400 frames. Each frame is 689x582 pixels in size. It seems like eog is allocating memory for every frame all at once when opening. This theory is supported by these facts:

1) It takes half a minute to open the file.

2) If each pixel uses 4 bytes, the total memory needed should be 4 * 689 * 582 * 400 bytes = 610 MB, which is close to 1.2 GB.