It depends on the size of the photo files you are sending but the answer should be "probably not". Typical image file sizes are around 5 megabytes, and even that tends to be an upper limit, so 60 or 70 of them total in the region of 350 MB, ie a sizeable chunk of your allowance but so long as the rest of your usage is fairly reasonable not enough to threaten that overcharge.
On a technical note, if you are giving the files to Truprint's website then you are "uploading" the files rather than downloading them. Here it doesn't matter as BT's T&Cs for broadband limits refer to "10 GB of internet use" rather than specifically a downloaded data limit, and I expect this is typical, but it's a distinction worth bearing in mind in case it ever does matter.
And finally, at the risk of advertising, BT is currently offering a subscription to unlimited broadband at the same price as its 10 GB limit package, although this may be for new subscribers rather than existing customers. But could be worth checking out in the new couple of days, as data usage limits are a real pain to have to think about.