I see that Acadia made the claim that,

thumbails that you upload with an image are 250 x 250 pixels in size,
to a maximum of 15,000 bytes.

Actually, the gallery upload page explicitly states that,

These Are the Allowable Thumbnail Size:

100 x 100 px (minimum)
200 x 200 px (maximum)
15kb (maximum, no minimum on the file size, just cant be larger than 15kb)

Therefore, 250 x 250 pixels wouldn't be acceptable. 

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Martin