There are several plot holes in this episode:

If Greg noticed that they weren't standing the same way they were in the original picture, why didn't he realize that Jan didn't have her glasses when the first picture was taken? He had been looking at the picture for a long time while trying to glue the frame back together so he could have memorized where they were standing (a detail Mike might not have noticed since may not have seen the picture since it was first taken), how could he fail to notice that Jan wasn't wearing glasses?

Why didn't Jan herself remember?

The biggest problem, the one that has bugged me ever since it first aired, is that upon seeing Jan with glasses in the picture, Mike immediately pulled Jan aside by herself and asked her about it.

Just because Jan's glasses were the most obvious difference doesn't automatically make her responsible, all the kids would have had to be in on it and since Greg was the oldest, he would have been the most responsible and would be the logical one to ask about it.

I wonder if Robert Reed objected to Mike's apparent ESP...

Good point. Why did Mike pull Jan aside when he had no idea why the picture was different? For all he knew, the boys could have ruined the picture playing football and hitting the picture. Or Alice could have dropped something on the photo while reaching for an item on the shelf in the garage.

Another observation, if I may ask here, why was there no GLASS over the picture to begin with? A professional photo usually has glass over it to protect the picture. Had there been glass, the picture might have been saved from Jan crashing into it with her bike. The glass would have broke, but probably would not have damaged the picture. I had a large picture where the glass was shattered, but the pic was untouched.